Hello dear
I understand your concern
First make sure than your period is regular.
Day one is the first day of the menstrual period and the last day is the day before the next period begins.
Ovulation happens about two weeks before the next expected period.
So if your average menstrual cycle is 28 days, you ovulate around day 14.
So do sex from the 10th to 20th day of cycle.
For better penetration keep pillow under back.
Eat healthy diet, drink plenty of water, do regular exercise, maintain proper pelvic hygiene.
If problem persists then detailed investigation of your and your partner will require by consulting the
infertility specialist.
Hope this may help you
Contact further if follow up needed
Best regards
Dr. Sagar