Could I Be Pregnant?

I always have heavy periods that last a week. I thought I began a new cycle on Monday bc I had light brown spotting. That is all I had was light spotting the last two days, now today, nothing? Could I be pregnant? Please keep in mind my 21 day progesterone was low and I tested a week and a half ago and it was negative. I know the best way to know is to take a test, but I've been battling infertility for 18 months so it's painful to test. Thanks.