The best advice I can give you is to hang in there and sweat it out. I'm at University myself and it is hard work. But the rewards after you have a degree outweigh the hard work you're going to have to put in. It seems as though you've just taken your January exams and you feel that they didn't go as well as they should have done.
Well the academic year is far from over, you're only half way through it, so you've got plenty of time to get ace your next exams in the summer. The key is getting yourself organised, planning your revision strategies and managing your time. Your personal tutor at University will be able to give you good advice on this sort of stuff.
If you feel you don't understand something or need more help, then go and see your tutor. Don't struggle by yourself burying your head in text books, it's a lot easier when somebody explains a difficult concept to you than trying to learn it yourself.
Make sure you also do activities which get your mind away from University and studying when you can to give yourself a break. Go to the gym, knock about with a football, or even go for a walk somewhere. This will ensure that your mind stays fresh, well thats what works for me anyway.
All the best with your studies, and don't worry too much as well cos stress aint gonna do nothin good for ya.
Take care