Promoore, seeing how you replied on the other post very similar to yours, why don't you take the pressure off of having to "finish" when you have sex. That way your girlfriend doesn't have to go into sex dreading your reaction at the end. It's probably stress or psychologically related (boredom, routine, habit - have all become monotonous perhaps?). Try addressing that by trying something new with your girlfriend. Spice things up and relax. These things tend to get worse the more you worry about them.
Take some time to read through other posts on here - this concern seems to have been vocalized few times times recently.
As for the oral sex, try reading this post:
http://www.medhelp.org/posts/show/349533