Spotting cd 21

A little background, I have PCOS and did a round of Follistim for an IUI we did back in august. After I was put on BC for a cyst. Since then I’ve taken a break due to anxiety but I started taking inositol in September. This month on day 21 of my cycle I went to the bathroom and had bright pink/ light red spotting and then spotted brown for two more days. Any idea what it could be? I have cycles that average about 35 days so it’s way too early for my period. I usually spot beforehand but only a day or two before.