Is there something wrong with me?

Hey. Im a 17 yr old boy and I started having sex about 8 months ago. The first time i had sex I lasted 40 min. Now eight months later, i last about 2 and a half to 3 hours. However, sometimes during sex I lose my hardness for no apparent reason. After a while when i get bored and really really want to cum during sex, it takes me about 10-15 min of extremely vigorous sex. Could this be a problem?

Btw, when i masturbate I can come in about 3 min if I want.

I've never heard of that before, usually guys have a hard time lasting. Perhaps it's becuase your not turned on the right way or you have blood issues.

I actually think it's because you're having too much sex. Try Going a week without sex or masturbation. I bet you'll cum very fast after that.