Chemical pregnancy or irregular cycle?

Hello everyone. Would appreciate your help here. I was in day 17 of my cycle yesterday when I started bleeding. It’s heavy and I’m passing some clots. I had a little bit of cramps as well. I’m wondering if this could be a very very early chemical pregnancy or just irregular period. My last period was quite light and barely lasted for 3 days.

This happened to me another time last year. Both times, twice daily ovulation testing from day 12 showed no peak or even high results. I normally ovulate in day 13-14. Did I simply not ovulate this cycle? Could it be caused by hormonal imbalance? I got pregnant the cycle after last time this happened, but had a MMC in week 10. Since my MC, I had two regular cycles where I ovulated. But we were waiting a bit.

I also have Hashimoto’s and hypothyroidism, and am on levothyroxine 100 mcg.

Thanks! ❤️