I'm from Britain and I'm not sure if going to our National Health Service will be much help. Althought its free it doesnt provide any mental health care, that sort of stuff if private.
Sorry, don't know where you live, In australia visit a GP to get a referral to a psychiatrist who can talk to you but you will unlikely get a diagnosis straight away unless it is blatant as. In America, unless you have insurance of some kind, and hopefully obama will organise that, you may have to go to some crappy free clinic, if you have insurance it probably (like most american policies) would be unlikely to cover psych treatment. If you have money pay for it. Sorry can't be much help with it if you are American.. If you are british, you're fine, just go to the doctor and he will take it from there.
A family member or if you don't feel comfortable a counselor could refer you to a psychiatrist who could do a further evaluation. It would make sense to keep a mood tracker so you can keep track of what's going on and then you could print out the results to them so they could further understand it.