go see a psycHOLOGIST... they will try to talk to you about and help you get some shit off your chest... they are trained to do so but will not prescribe you medication like a psycHIATRIST would.

... but if you are really honestly getting depressed afterwards, it maybe a chemical thing going on in your brain dealing with the re-uptake or elimination of endorphins or other neurotransmitters that are released upon orgasm. talk to someone dude because sex is just too damn good to be feeling like that afterwards. good luck.