Days before period affect milk?

I noticed the last 2 days my baby wasn’t filling up her diapers as she regularly does. & Then this morning I noticed it was back to how normally full they usually are. When I went to use the restroom I noticed my period has returned. I’ve heard about periods affecting some women’s milk but is this going to be an every month thing? Will my supply drop every month when my period is due? I don’t know how to feel about that. & I can’t offer formula because she will not take a bottle & the formula makes her gag. I am almost 7 month pp, any words of advice I appreciate. Also I am not on any birth control yet but will start the mini pill soon, will that have any affect on my supply as well?