Drastic mood shifts. Normal or i'm sick?

I've always bad at handling stress but I used to think it's normal, I panic at slightest of things and then won't be able to do anything, especially in exams. But recently I've been worse, I can't focus for more than a minute, I'm always distracted, always irritated, I snap at people for minor things, I get very angry very soon even at small things. I get upset even if nothing happens and I remain sad and I don't understand why, I keep crying during such days, nothing makes me feel better, I try to cheer myself up but nothing works. After some days I get back to normal. Some days I'm very normal and upbeat but on others I don't want to get out of my bed. I get offended very easily and later realise that it was nothing. I find it hard to trust people, I can't take criticism, I'm optimistic but a small setback and I can't do anything I stop functioning, lose focus, efficiency everything. Lately, this has affected my studies a lot. I want to be normal as before. Is it normal or I'm sick?