birth control reducing milk output?

Any pumping moms find that the mini pill reduced their milk output? I am struggling here and don't want an IUD, but I am finding my son feeds more often and I am pumping 50% less than before. He is gaining weight (slowly) and since 8w he only has one poopy diaper every 3 days (used to be 5 a day). I know this can be related to his growth, and he still has plenty of pee diapers but I am still worried. Anyone else going through something similar? Thanks!