Lactation boosting tips needed!

Ftm here. My baby is almost two months and he already eats 8 oz! I can’t produce enough breast milk for him so I’m adding formula however all the formula we’ve tried had been making him constipated. Even the stuff from the doc does it. When he has nothing but breast milk he’s regular. The doc suggested I solely breast feed him so I need tips on how to produce more milk!! I have pump it up vitamins and I drink a body armor every day and lots of milk and water throughout the day.