Pumping/milk supply question

My baby is 3 weeks old, & ive been EBF... I've also been pumping twice a day (After 10 AM & 10 PM feeds) to save milk for when I go back to work full time. I've always gotten around 5-6 ounces with every pump session... until the past 3 days! Now I'm only getting 1 ounce, maybe 2. Is my supply decreasing? I know my baby is still getting enough because he still feeds for 20-30 minutes & is satisfied... but how come I'm not pumping as much? And I'm worried about eventually not having enough for my baby! So I need to start doing everything I can to increase my supply?