Milk supply and birth control

Brittany
Is anyone on birth control and they see a decrease in their milk supply. I started the mini pill at 6 weeks pp and now at 18 weeks my supply is lower than ever. While at work I'm use to pump close to 15 oz in 8 hour period but now it's barley 10 oz.  I have heard 4 month leap effects you and baby but wasn't sure. Anyone else having this problem??