problems while on birth control

Hi all, so I've been on previfem for about 8 months. I am never late on taking the pills and have never forgotten to take them. My periods used to be normal before starting birth control and ever since being on it my periods have been acting up. Usually I always start while still on the active pills. Like right now I just started my period and I still have a week of active pills left. There's only been about 3 times that my period has come on the normal inactive pill days. I've also noticed that my periods seem to be heavier and more crampy. Has anyone else dealt with this before? What could be wrong with me? Should I just skip the inactive pills if my period comes while I'm on the active? I'm just really concerned that there could be something wrong with me. Thanks so much for any responses!