Try this: Find some chics on the net that are damm hot to you. Whack off till you cum. Do this for a few days, and make sure to be getting in enough fats. Like from peanut butter. Now, after 2 or 3 days of this, don't whack off for at least 4 days. Just tell your girl you strained a muscle in your rib cage. In the mean time, do some heavy squats. BURN those legs and don't worry about it, it'll come back. BTW, this might sound messed up, but when you screw and aren't married, sometimes it's tougher to perform and the sex isn't as good...may only come through on a subconcious level for some.
BTW, you don't have to get out of bed to do phase I. In fact, stay in bed more and sleep more.