I've noticed several times if I took a pain pill(lortab or vicoden) and had sex later, it took forever. It wasn't planned that way. It just happened. Also, frequency has helped me in the past. If we have sex daily, it usually takes longer and longer. IMO, marathon sex isn't always what it's cracked up to be. If the wife and I go at it for a while, she will not want it again soon. She says she's a little sore from the long outings if you will. Overall, I think I like to measure sex in quality not quantity. I wouldn't worry about going forever as long as each of you are good and satisfied at the end however quick or long it takes. An intense spontaneous quickie can be great