The best time to conceive is just before ovulation. Do you know for sure that you're ovulating? If so, has your partner had an evaluation to verify the health of his sperm? In a typical 28 day cycle, you're probably going to ovulate around day 14, which means you're most likely to conceive in the days leading up to day 14, on day 14 itself, and maybe even day 15. If your cycle is longer, you probably ovulate later. If you haven't had any sort of medical evaluation, that's where I'd suggest you start. Good luck!