Is it normal for milk supply to drop while you're having your period?

Agreed - it's due to hormonal imbalance. The return of our period after giving birth has a great impact on our milk supply (which I also experienced and got bothered too!). Few days before our periods start, our blood calcium levels drop which can either or both: 1. Your milk supply will drop a bit 2. Your breastmilk flavour can change and baby will notice it as well. Once milk supply lessens, baby tend to latch more frequently but the change in flavour may cause baby to latch lesser. But according to the article below, this is just temporary. :) https://www.babysleepsite.com/sleep-training/menstrual-cycle-affects-baby-sleep/