In my experience, I have found that how long I last is 90% psychological, and it may be that way for you too.
If I go into bed excited and all geared up for sex and it has been a while, I find that I come very quickly.
However, if I'm very calm and not worked up about getting laid, I can go for a good 45mins-an hour. A bottle of Vodka also helps with this
I think thats all the advice I can offer. Hope things work out!