20 and constantly worried

I'm 20 years old in my second year of university, I should be enjoying everything right now because I am surrounded by so many amazing people who love and care about me. Instead I worry everyday about everything and everyone and seem to be falling down a black hole every time I try to be positive. I used be such a positive person who would always be optimistic about everything and smiling all the time. Now I can't get out of bed and when I do I end up either having an argument with my family or friends or crying. It's so difficult because I never used to feel like this and I'm constantly frustrated that I can't be that person any more. I don't know what caused it but from an early age people have bullied me until college years which made me discover myself and like who I saw in the mirror. However,this semester has been very stressful and some people have knocked my confidence, which has made me question myself and my aspirations. I feel trapped and I have no excitement to do anything any more. I study musical theatre and I should be excited and enjoying every minute of the opportunity, I have been given but instead I worry about the little things. Nothing used to affect me this greatly and now my behaviour and attitude is affecting everyone around me. This is something I can't bear to see. Everyone's been trying to help me and I'm taking St Johns Wort herbal tablets which help me have better spells. I hate to be the burden though, I'm the one who brings the happy mood down and people tell me I must ask for help but I don't want to be a nuisance, they have so much more important things to be doing.

Some days I have good spells and then other days I have bad spells where I won't talk to anyone or do anything. It's affecting my friendships with people and this is something I can't cope with. I get so paranoid and irritated with my closest friends which upsets them greatly. A few days after I feel so guilty for even questioning our friendships but then the repeat happens. I just feel like I'm in the way and what's the point. It's terrible to think a uni student is not drinking but it does me no good, even the very rare glass of wine at the weekend. I want to be able to have all the good times again and laugh. It makes me so tired just trying to be me everyday and I just need help.