My baby is 9 1/2 weeks old, I tried breast feeding, couldn't produce enough so I had to supplement,…

My baby is 9 1/2 weeks old, I tried breast feeding, couldn't produce enough so I had to supplement, well he likes the bottle better than the breast during the day and he'll nurse at night. he usually takes 3 1/2 to 4 ounces. He is on both formula and breast milk right now. I can only ever get 2 1/2 to 3oz pumped, any advice on increasing supply? My OB put me on some pills that I had to take for 2 weeks but only made it through 1 due to the side effects. I'm trying to pump every two to three hours. Very frustrated at this point.