one day period/spotting

ok ladies i need help.

im on synthroid which has finally gotten my cycles to a regular 25 days same time same day for months now! ive never had this ever!.....


i still have dark brown/black spotting for 2 to 4 days before red AF starts (dr says not to count it as AF).

for the past two months my period has only lasted one day and completely nothing the next day. its dark red with clots not the bright red. i would say heavy flow for the day and horrible cramps on one side i was almost crying yesterday. tylenol didnt touch it but high dose ibuprofen helped. now nothing. what is this? what hormone causes this? my 21 day lab was normal showing ovulation (got it day 17)

has anyone had any of these things happen?