What Causes Back Pain And Vaginal Spotting After Starting Microgestin?

Hello I have been on birth control pills for the past three years currently I have switched to a generic brand and am experiencing horrible cramps and chills and back pain with nausea. The bcp that I am currently on is microgestin fe 1/20. I started the iron pills yesterday and have felt like this from 6pm on. When I was on lorstrin I never got my period now I am spotting lightly. Is this normal?