Period after pregnancy while on birth control

I had my baby on March 30. I went for my 6 week check up on May 11. My post partum bleeding stopped completely around 4 weeks. I thought I was getting my period on May 20. Turns out it was spotting. This went on for about a week until I got my actual period on May 27. I went back on the pill (Sunday start) and my period lasted for 7 days. Fast forward to June, I should be due for my period this week (Monday or Tuesday) but I started spotting again last Monday...a week before my expected period. Prior to getting pregnant, I was on the same pill for for about 12 years. I would only stop while trying to conceive and obviously during pregnancy. While on the pill all those years, I never experienced spotting or break through bleeding. When I had my first child 3 years ago, my period was back on track about 8 weeks post partum. I wonder if this pill no longer agrees with my body. Perhaps I need to try a different one? Has anyone else experienced this? Let me add that I am not breast feeding.