I just started my first period since starting taking birth control pills. It started with some cramping, somewhat painful, but typical for me. My period usually starts off heavy but it had been pretty light so far, and after changing my tampon I noticed two kind of large white/grayish blobs mixed in with the blood. Does anyone know what this could be?? Should I be worried?

Also, I am taking lo ovral pills, and my period didn't start until the fourth day of taking the non-active pills.