Have you tried timing your cycle as best as you can? One sure shot way would be to figure out your fertile days and have sex every other day during your fertile days - or really, as much as you can. Also try keeping your legs elevated (maybe a pillow under your butt) and keep still for a few minutes to increase the chances of the semen flowing into your cervix.
I understand there are some fertility blends etc. available in the market, but I cant personally vouch for any of them since I haven;t tried them. Hope this helps!