I don't know what to tell you man. When I'm first dating someone I'm usually busting through my pants at all times. I don't know if you masturbate a lot or not. But if you do, why don't you stop cold. That way you'll be popping wood all the time no matter what you're doing. Also, you could be putting pressure on yourself. At one point in a relationship I was in I started having trouble getting it up, and I'm not going to lie, I'm usually hard about 60% of the time anyway, so it was pretty weird. She thought I was getting bored, which wasn't the case at all, but then I started worrying about it, and the problem just got worse. Eventually I went back to normal though. Just try not to think about it and see what happens.