Be sure that you are not
having sex TOO often, too. For men, ejaculating more than once per day
can actually reduce the sperm count. So, for example, it would definitely not be a good idea to have oral sex first, and then vaginal sex later.
I must say that I doubt this is the only problem--if you were my patient, I would also run some tests, such as ovulation predictors, semen analysis and an HSG to determine whether there was any blockage in the fallopian tubes.
I hope this helps!