spotting/cramping a lot when on BC

I am preparing for a frozen transfer in January. My RE put me on birth control for about 30 days. I am on day 22. I was given strict instructions to only take the active pills (skip the placebo pills), which I have done. I have been spotting and cramping for the past 2 days. It's been brownish, not bright red. But it's only been getting worse and seems to be getting heavier. I just don't understand how I am starting my period if I've only taken the active pills?? Girls skip the placebos to skip their period all the time. I don't get it.  I'm sooo afraid it messed up my FET. Anyone have a similar experience?