What are caused by spotting during active pills and bleeding in a 7-day break when taking birth control pills?

In August, I gave birth by caesarean section. After 7 weeks I got 1 menstruation, and after 26 days the second. On the first day of my second menstrual period, I started taking Elin. The whole time I took the first package, I stained. During the break, there was more abundant 4-day bleeding. It ended and bleeding and spotting. When taking the first tablet from the second package, spotting began again. He is not taking any other medications. What could be the cause of this?