Why can't I just be happy?

Hello, I am new to this and have never spoken to anyone properly about how I feel, but slowly things are just getting to me that I find myself crying myself to sleep almost every night. I am constantly feeling down and alone and whenever I go out my heart races and I start to feel sick and scared and just race to get back to my flat.

I'm a new student at University and am 18, and it's my first time ever living and being away from home. I have been bullied for 14 years so have never really had friends.

One year the bullying got so bad that I was chased down the street by a gang who wanted me dead, and as a result I found myself hiding in a pub toilet. Due to never having any friends, I never left my house. My mum and dad along with my little sister are my only friends, which is great I suppose, until you move halfway across the country from them for uni :(

Starting from the age of 12-13 after dealing with bullying for so long, I started getting these thoughts of "Maybe it's all my fault? Maybe I'm asking for it and deserve it?". I then got to the stage of Cutting myself and tried committing suicide about 9 times, but I was never strong enough to end my life, so cutting was as far as I could go. Then I started abusing myself verbally and physically, calling myself a stupid bitch that no one likes or loves, hitting my head against the walls until I would feel dizzy and sick. I could never tell my parents about this, it would break their hearts, and I couldn't have that burden on them!

I then got a new boyfriend when I started Sixth Form age 15-16, but then he tried pressuring me into having sex which I refused and kept pushing him away until I could run back into the school. I was terrified but I couldn't tell anyone. Then he ended the relationship through Facebook messenger saying he deserved a better woman and that i was nothing but a pathetic child who wouldn't even have sex with her own boyfriend. I felt disgusted by everything he was saying. I had not long turned 16, and I would never EVER think of losing my virginity at that age, especially after being in a relationship for no more than 3 weeks :/ But at the same time, my heart shattered. I thought he loved me. I though I found someone who cared and that I could confide in without breaking my parents hearts. He hurt me so much I resorted to cutting myself again. 

Then, in my final year of Sixth Form aged 17, someone new walked into my life. He was so perfect and loving, a true gentlemen. i loved him so much, and I still do. I was able to confide in him about everything, including self harm and suicidal thoughts. He helped me stop cutting and gave me hope again. But then I had to make the big move to Uni, miles and miles away from everyone I knew and loved. He told me it would be okay, because I'll be working to a brighter future and the three years will fly by.

When I moved to Uni in September 2014 I was so scared and lonely, I broke down and just wanted to go back home. At 18 (current age), I can't cook or even look after myself properly. I just wanted to give up on my future right then and there. I didn't see no point. I started cutting again after just under a year of stopping. When I told my (now) Fiancé, it broke him. I let him down so much, but I just wanted to die so badly. My flatmates were bullying me, I had no friends in class, I was completely alone on the other side of the country with only phone calls and Skype to contact anyone, but that's not the same as a physical hug.

I promised him I would never do it again, but to this day I still find myself crying to sleep and having bad dreams and hallucinations at night. I struggle sleeping and from chronic pains in my stomach which Doctors believe is Kidney Stones, but Idon't get results back until 9th of Feb, and even then the Doctor said I might need an operation. I'm terrified. And every time I start to feel even the slightest bit happy, something always happens to rip it away from me again. I still have that urge to cut myself, to relieve the emotional pain inside my head. 

I spoke to a Psychiatrist before about this and they said they will get back to me, but it's been two years and I haven't heard a thing back. I decided to start looking into things and found that I share so many symptoms (pretty much every single one) of Bipolar Disorder. I have the major highs for absolutely no reason and feel so amazing that I've had people ask if I've taken drugs (which I never have). I feel over-confident like I'm better than everyone else in my class and receive amazing grades. My thoughts race and I can never stick to just one task, i get easily distracted and talk so fast that my family ask if I breath out of my ears (which I find rather funny).

But then I hit rock bottom. I feel low, useless and pathetic. I look at my grades and am 100% certain they aren't good enough and that I am nothing but a stupid failure. I feel like I'm letting everyone down. I fight my suicidal thoughts so much and have to put away every single sharp object in my room and fight off the need to self harm. I get so angry and irritated easily and take it out on those around me. I've lost interest in the things I once loved and even sit here thinking "why am I even at uni? I'll never get my dream job! I'm wasting my time as well as everybody else's!"

Ever since I first spoke to someone about how I felt, I never did it again after that. They just left me! When I really needed them! I've never been formally diagnosed by a Doctor but I'm pretty sure that these arguments I have with myself and the fight to stop myself from doing anything stupid isn't right!! All I want is to be happy. Why can't I just be happy? :(

I'm so sorry that this is long winded, but I've been holding so much in for so many years. In fact, this is the shorter version :/ I just needed someone to talk to. I just needed to get this off my chest without hurting anyone I love. 

Why do I feel like this? :'(