This is really a barrier I need to overcome.

When I kiss girls I ALWAYS get a big fat boner, even some precum. But when sex is about to happen, my penis is like "yo man I'm out of here.".

I am 20, at a healthy weight, I eat right and I've started lifting. I do not watch porn since months, masturbate once a week.

I tried viagra but it didn't really work for me.

What can I do to make my dick stay hard during sex? I'm just really annoyed and want to find a solution so I can stop worrying about it.