Menstral cycle off

I have hypothyroidism and take medication for it but it seems that my periods are always off for some reason and it's hard for me to track my ovulation days. We're not "trying" to have a baby but I would like to know my fertile days. I've talked to my dr about it and she put me on birth control to regulate my cycle, but the birth control makes me sick. And my biggest fear is that I'm not going to be able to have children. Does anybody else have a thyroid condition and have children?