BFP CD12 then BFNs?

So I have PCOS. I was given my first round of clomid in June/July earlier this year with no luck. Didn’t even get a period afterwards for a couple months but I thought whatever I had other things going on. Then when things settled I decided to do another round of clomid. My dr prescribed me provera which I took and had a period from 11/12-11/18.

I was supposed to do a scan to see how I was responding to clomid on CD14 ( which would’ve been Thanksgiving day when they were closed ) so they decided to have me come in on CD12 instead. When my dr did the scan he said there were NO dominant follicles and I once again didn’t respond to clomid. I was really bummed and thought I’d waste the pregnancy tests I had just bought and was saving. when I took the first response I saw a line right away and it kept progressing. It was a clear bfp, but all tests since have been negative. I only got that ONE bfp on CD12, the same day I had an ultrasound and was told It didn’t work. Was it a bad test? I am now CD16 and still nothing.