Help! My milk is disappearing!

Hey ladies!  I am 3.5 months PP and for the past couple weeks I noticed my milk supply has been lower.  My LO will punch my breasts or generally get frustrated when the milk runs out before she's ready for it to.  Also my let downs sometimes take a few minutes and never had before.  I thought it was because I've been trying to lose weight and lowering my calories seems to make my milk supply suck, so I stopped that and my period started today!!!  My boobs feel completely empty and my little girl gets mad at feedings because it takes forever for a let down and then there's not even as much milk as she would want.  She is still having plenty of pee and poop diapers,however I'm not sure she's gained much weight in the past couple of weeks.  What can I do to get my milk back?  Will my supply return once my period is over?  I am so upset because I want to breastfeed her for a year!!!  TIA!!! 😔