FET bleeding

I just transferred today (November 17) our fourth frozen embryo this year. Everything went as usual and now i started spotting, only few hours later. I don’t know how is that possible, it is not my time to get a period yet, ut us CD21. Also calling the doctor. As this really doesn’t seem normal. My clinic has unmedicated FET, so basically you are just being monitored via ultrasound and no medication at all. I had success with my 1st FET in 2020 (transferred one and got twins).