Breast milk production increase

What can I do to help increase my milk production? My baby is 6 weeks old now and I’ve had to give him formula the last few days because I haven’t been producing enough milk. I have been able to pump maybe one 2oz bottle all together throughout the day. My breast have decreased in size so I know my milk has decreased a lot. Also I have to use a nipple shield when I do breastfeed. I’ve tried eat oatmeal, lactation cookies, water,getting plenty of rest. What else may help me?