Anyone have any ideas what could be wrong?

Hey there, im a healthy 20 year old male and for the past year or so i've been having erection libido/problems which come and go every few weeks and whenever this occurs it is accompanied by frequent urination and excessive thirst.

I went to the doctor and he is no help at all, he basically said my only option is v!agra LOL...ridiculous. I was tested for diabetes and am fine...anyone have any ideas?

thanks.