Side effects of mini pill?

I've been on the mini pill (Feanolla) since July. It's been great and completely stopped my periods. For the past few months I've started to notice something, around the day I would be due on, I'm spending a good few hours with cramps and being sick. Like a good 5 hours and then I'm absolutely fine, don't feel sick at all. I've been on different contraception for 6 years and never noticed this with any other.

Has anybody else had this as a side effect or heard about it? I'm not sure if it is the pill, but a pattern is forming and that leads me to wonder if it's possible that because my body can't have a period when it wants to, I'm just starting to be really sick instead? Thanks!