Need some advice please.

My LO just made 5 months & I have pumped & breastfed. I have had to give him some enfamil enspire. So he is like 80%ish breastmilk & 20%ish formula.

I have noticed the last 2 days my milk supply has dropped so when I PUMP. I normally pump anywhere from 6-8 oz first thing in the morning. The last 2 mornings I’ve only pumped 4oz. I’m not about to get my period because I start one the 13th or 14th of each month & I notice my milk looks more “watery” when I’m about to start.

I just don’t know what to do! I’m not ready to stop! (Sorry if that sounds selfish. He’s my 3rd boy but first to be able to breastfeed)

When he nurses at nigh he sleeps all night 9pm-4am & he seems full mots of the time during the day.