I have been trying to conceive for 18 months. My doctor found a 1cm polyp in my uterus. It causes the uterine wall to have a ripple in it, so the egg can't implant into the wall and grow. My polyp was at the entrance to my fallopian tubes, so nothing was getting in!
I've had a hysteroscopy and polypectomy (i.e., removal of polyp). Polyps can cause miscarriage, so my doctor said to remove it now to reduce potential probes later. Mine and my husband's other fertility tests (sperm, ovulation, hormones, egg production etc) were absolutely normal. Hope this helps!