Erectile Dysfunction

[jaycas]

I am a very fit 20 year old male, i am in the gym every day, run 3-5 miles every day have no cardiovascular problems or psychological problems, ive never had erection problems until about a year ago. my relationship with my girlfriend of four years has really sufferred in the past year due to this. She use to walk into a room and i would pop wood almost instantly but for a year now ive been barely able to get an erection sufficient for intercourse. It will get hard for a good minute or so right about until i try to put it in and then it goes flacid, or sometimes i can get it in and it will go soft inside of her. I have tried everything possible ive been to the urologist and he said my blood flow is fine and im a healthy 20 yr old and should have no problems. I went down to a specialist in ny that wanted to put me on caverject but thats not a solution, its a quick fix to a bigger problem. I tried using various libido enhancing supplements: extagen, orexis, magna rx, etc. etc. All to no avail. I just recently found out that my father and my grandfather both have had pituitary tumors and am wondering if pituitary tumors are hereditary and that may be the cause of mine
Because they do control all of your hormones including your Luetenizing Hormones or sex hormones. Is this a possibility or is it maybe something else.. maybe theres some type of disorder that causes the penis not to hold all the bloodflow?