any exclusive pumping ladies out there?

S
I've been trying to BF but my son (4weeks) had a tongue tie and wasn't getting much milk out (which we recently found out), so now I've been supplementing with formula through a tube while I BF to increase his weight gain and stimulate my milk production. However, even though his tongue tie has been fixed, the latch is still off, he wont open his mouth enough and he gums my nipples, the pain is excruciating, I'm thinking of EPing instead, and at the moment I'm producing between 1.5-2 oz in my left breast and 1-1.5 in my right. Which is a lot better than where I was last week (1 in my left and 0.3 in my right)! 
How often and for how long do you ladies pump? Any other tips?