2nd child first time being able to BF

I had my daughter June 11th my milk started to come in the 14th/15rh so Friday and yesterday. I breastfeed/ supplement. I’ve been giving her the breast but her latch technique is a little off she sucks like a vacuum lol. She eats but not much it’s like an Oz but she is an around the clock eater if that makes sense . My bobs hurt so bad , I’ve use warm clothes while trying to pump when I pumped to relieve some of the pain it barely work . I have knots in my boobs and I pumped ALMOST an Oz from both boobs combined . Is this normal , am I pumping too early . any advice is acceptable