Sudden decrease in breast milk

Hi 👋, so from this week I’m nothing I’m producing less milk and milk looks less fatty too after pumping. I was able to pump 1 litre and 50 ml a day after pumping 4 times a day for 20 mins. Now I’m only getting 800ml a day for same pump durations . My baby is gonna be 3 months next week. Please help. I only breastfeed twice a day sometimes n some days not even once and was still able to get that much milk. All of sudden from a week I’m noticing a change .

Only things changed is I’m starting to healthy n walk on treadmill for half n hour a day.