I Recently Went Back On Birth Control At The Beginning

I recently went back on birth control at the beginning of february. The pill that lets you have a period every three months. I have been spotting off and on ever since i went on it and in the past few weeks i have been bleeding pretty heavily and in the last few days i have been having the worst cramps i've ever had and they are making me feel sick. i saw my doctor two weeks ago and she told me to just keep waiting it out but now i'm getting concerned.