Fertility concern. I conceive naturally?

I tried to conceive for 6 months and then visited to doctor to get an evaluation done in July 2018. I was asked to do some blood tests (FSH -6.59 and AMH - 2.45) and an HSG (no blocks in tubes and uterus shape is fine) as a preliminary test. Later in August in a follicular scan, something cropped up in the uterus and I went through a hysteroscopy. There was a polyp on the exterior wall but besides that everything else seemed normal. Then for two cycles I took fertyl and went ahead with iui but both the attempt failed mostly because my uterus lining wouldn't grow beyond 6mm. In my last cycle, we decided to go natural and ovulation occurred on time. But my lining wouldn't grow beyond 7/7.2 mm. In my current cycle I am on Newmon R injections and progynova and plan to get an iui done only if my lining reaches 8 mm. My doctor suggests that from next cycle we will go for a FET. My question is since everything else is normal can't I conceive naturally?