Talk to Gynecologist on Periods Flow Issue

My periods didn't come in December, just spotting occurred. Then in January it normalized completely. The flow lasted 7 days and was normal, heavy at the start then lighter. Then in February, March, and April my period flow decreased to only 1 to 2 days and the color also turned pink. The doctor told me to get a pelvic ultrasound and everything came back normal. Then the doctor ordered FSH, LH, and thyroid tests and those also came back normal. Now in May my flow has improved somewhat and the color has also turned red, but it is still not like the flow I used to have and it is still less than before. I also have B12 and Vitamin D deficiency. My B12 was 127 and Vitamin D was 10 and treatment for both is ongoing. But I am not understanding the reason for the reduced flow and I want to know if any more tests are needed now.