Some good advice here. It isn't too late to get help - definitely see your GP. As someone else noted two issues here - first, and most important, your health. So see your GP, consider medication, but ask about side effects if you're concerned. You may find they either make you sleepy, or stop you sleeping, for a few weeks - but they might not.
Second - mitigating circumstances. As someone else said - explain your history to your GP, see what they say. Explain that for Uni purposes you could really do with a letter of diagnosis 'to whom it may concern', and that it would be really useful if it said something about your history ie that your depression hasn't just started, its been ongoing. He/she might also add - if you decide on meds - that they'd appreciate teh Uni ttakign account of the fact that whiel you've been prescribed medicaiton, this is 'unlikely to take full effect for some time, and so X's preparation for examinations is likely to be adversely affected.' I would also register wiht studen disability services (if you haven't already) and give them a copy of htat letter as evidence, and then apply for extra time for your exams for a start, and anything else that would help, like 'consideration'.
Apologies for the typos - in a bit of a hurry.
Good luck with everythiing, includign exams, but rememebr that you and your mental health are the most important thing.