Supply dropping before period? Or pregnant...

So I’ve noticed these past few weeks my supply hasn’t been able to keep up with my baby. I wasn’t having problems until I returned to work but I’ve tried EVERYTHING to increase my supply. I was able to pump 4-5 oz before, and suddenly I’m only able to pump 3? pumping 3 oz in an 8 hour shift which is consistent with babies BF schedule at home on days off. But she’s now taking 5oz bottles and I’m not making enough? I was thinking it was because my period was about to start.. but my period is 7 days late.. this would’ve been my 2nd period post partum so definitely haven’t gotten a regular cycle back yet.

My question is how soon before your period did your milk supply drop? I know period hormones can affect supply, and it definitely did my first pp period, but I don’t remember it affecting it this long before period IF my period is coming.. waiting a little longer to test, but curious how long before period you guys see milk supply drop.