A topical cream will not effect your ability to conceive.
You only have a 25% chance of conceiving in a given cycle so they fact you havent gotten pregnant after 3 cycles is very normal and nothing to worry about. If you dont get pregnant after a year of trying, make an appointment with your doctor.
By the way, be sure to start taking prenatal vitamins even though you arent pregnant yet.
Thanks so much for your post! Hopefully my BFP will come soon!