Wow that gives a new meaning to "slow-ish" 2 months.
Have you had this happen before?
There can be a number of things going on to cause this, like maybe to much sex.
Try going at it just 2-3 times a week. (go for walks or to a movie with all the extra time.)
Might try using a different style of condom may also help.
Everyday stress can be a factor as well, like bills or a job issue.
Even if you don't think of these things while having sex it can play a small part.
Talk to your partner about it as openly as possible, more you think it will affect your relationship the more likely it will.
Good Luck.
Chow-