What Causes Pain In Penis?

hello im am 25 year old and i have had my penis problem for about 6 month. I was having sexs with my girlfriend and everything was okay but the next day i was suffering shooting pains on my right side of my penis going from the tip right into the pubic area. i have only had sex three times since then because i was told i need to have plenty rest and take inflametery tablets which did easy the pain. Just recently i gave my penis 8 weeks rest with no sex or oral, so my girlfriend gave me oral sex very gently and again the next day i get thr pain but not as strong. It is really stressing me out now I can get a erection no problem with no pain and i can ejaculate no problem with no pain.
hope you have some good advise? lee