<human>: So I've been dating this girl for about a month. Everything was good until suddenly I stopped maintaining my "hardness". At first it was because I was eating a lot of soy. Now I don't know what the problem is. I get semi hard when we kiss & such but right before I'm about to put it in it goes limp. Although one time I tried my hardest to get a semi hard erection (hard enough to go in) & once I was inside it got reeeeeeally hard. I don't know what the problem is. I masturbated up to 6 times a day from ages 13-15 then I cut down to 2-3 times a day from 15-17 then once a day from then until I  met this girl. Now I masturbate maybe 2-3 times a week. Even then I can't get a full erection. Last time we had sex was about 3 weeks ago. I want to do it more often but I physically can't. What should I do? I'm 5'9" 140 lbs don't smoke nor drink. My diet is ok but no sodas or juice, only water. I take multi-vitamins along with garlic pills & vitamin B-12. I don't exercise but that's irrelevant imo because I could get erections in the past month & nothing has changed diet/ exercise wise. I'm going to try quitting masturbation cold turkey. Will no sex/masturbation for 2 weeks help? Is it the vitamins I take? Or is it deeper than that?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: I can get hard sometimes but not often. & when I do I can't maintain it. I take multi-vitamins, garlic & B-12. No drugs or alcohol. What's causing this?