My boyfriend has been having problems either getting an erection or losing it during intercourse. He's been to the doctor and they said he was probably just stressed but he recently has had much less stress and the problem still persists. He was a virgin up until a month ago so I was wondering if that might have something to do with it and the frequency of intercourse or if it might just be an issue of eating right and exercising. What do you think?
Assuming your boyfriend is under the age of 35, it would be very unusual for the erectile difficulties to have a physiologic (hormonal or mechanical) cause. It is most commonly related to factors such as medication side effect, alcohol or recreational drug use, or psychological concerns, including ambivalence about being sexually active (i.e. fear of STDs, getting a partner pregnant, the commitment implied, etc). Most younger men who have erectile problems are feeling pressured to have erections on demand, and the stress of "performing" results in loss of the erection.
He has only been having intercourse for a month, and probably is even more concerned than you about this right now. It is best to back off on the intensity and frequency of sexual activity so he is feeling less pressure to "perform"--it is best to work on making your relationship solid and trusting, so that occasional erectile problems simply is no big deal. Right now, if he's already been to the doctor about this, it is a very big deal to him. Once he can relax about the new relationship, he will have fewer issues.