I need answers !

So this is my second time around breastfeeding. My LO is 5 months . I notice , either before I start my period OR while I’m on my period , my supply goes down (i pump for work) so she’s stuck on my boobs .. then 2/3 days later my milk comes back A LOT(I have to pump all day long) ! My oldest , I guess since I was on birth control ? My milk never changed . But with my youngest , since I’m not on anything, I notice this a lot each month .

I absolutely have no problem pumping 10 oz in one session. It’s just these days I notice I can only pump 2 oz .

Has anyone experienced this also ?