Problem very weird!?

I don know whats wrong whenever im getting oral or im on top of him i always feel this sensation i start slowing down and gasping for air all of a sudden it starts feeling great like im about to but when i try or not try to let it out NOTHING! as soon as the sensation goes away it hurt me for him to continue giving oral or for me to keep having s** with him. Its like im satisfied and i dont want to have anymore and because it hurts me so whats wrong i mean its there but it dosent come out he even told me that i had to go see a doctor because that wasn't normal. One 1 time when i was playing with myself it came close but i felt tense it was feeling good it was about to happen but NOTHING! so what is it is it the partner i was with or myself. i think i have endo but i dont think that has to do with anything. So what can be wrong? or should i just give it time MORE time thanks