Hey doc. I'm 21, and in love with a girl I'm just friends with. I recently tried sleeping with a different girl, and found that I couldn't keep an erection during the sex. It was my third time having sex, and it's happened each time. I do masturbate regularly, so I believe I have E.D. I hear that vitamins can help treat it, but I'm unsure. Is there a type of medication I should be on to help with this?