I know how a lot of this stuff feels, due to the fact that I'm presently going through a depressive phase at the moment - as well as having been through them in the past. I'm taking antidepressants, so I'm not sure if the reason it's still happening with me is due to side effects of the meds, or if the meds aren't actually making a positive difference (I have noticed a positive effect, though).
In answer to your thread, you should see a GP about the problems you're having; they'll be in a position to medicate you/make referrals for you, if necessary.