Can't get off?

So Im still kinda new and just starrydd having sex with my girlfriend a good 2 months ago and I've found that I can't ever get off. It literally takes hours for me to get even close but I always lose it just before I get there. Whats more, I cant even get turned on by myself anymore. As soon as we start making out Im all kinds of turned on but by myself I can't even get the slightest bit wet, let alone get off no matter what I do. Any advice?