Problems with milk!!?

ok so my baby is 9 weeks old now and i am tryin to exclusively give milk to him. the doctor put him on formula suppliment because he was really small still but he seems to be allergic after 5 days of havin it) so now im just trying to feed him and pump to suppliment him with that but my milk supply seems very low. he'll nurse for a loooong time and come off unsatisfied. so then i'll pump in the morning and also pump in between feedings, and after feedings and at night after hes asleep (so nursing or pumping 8times a day). and my supply is very low..like 1.5 - 2 oz for 30mins of pumping..what do i do?? it wasnt like this before!!!