supply drop at END of period?

i’m 13 weeks pp and just got my first cycle in exclusively pump. my supply has been fine until

now im at the end of my cycle and just spotting for the most part but now my supply is taking a hit. nothing else has changed im still doing the same things as usual, same schedule, same hydration, same nutrition, besides im ending my period. i have heard before your period and the first couple days it could mess with supply but never the end of your cycle. is it my cycle ending messing it up or could it be something else?