Progesterone?

We did our first IUI in January and got my very first BFP. We were ecstatic but my HCG and progesterone both came back low (HCG was around 75, can't remember what prog. was), so my RE put me on progesterone suppositories. Unfortunately, my HCG levels dropped on my second beta. I asked my RE if the low progesterone caused the CP and he said no, that usually low numbers just indicate an unhealthy pregnancy but didn't necessarily mean that I have low progesterone or that I would necessarily have low progesterone in future pregnancies. He said that he could put me on progesterone after my next IUI if I wanted. 

I see a lot of people on here say they take progesterone after their IUI. I was wondering if most people's doctors put them on prog post IUI or only if they have low numbers. We are about to begin our second IUI cycle and I'm wondering if I should ask to be put on prog just in case? 

Thanks for any feedback you can give. Baby dust to all!