Good luck! My lo is 15 weeks now and we had this from 2 weeks until, well, it still happens occasionally now. Everything Sam's mum says is great, particularly about draining the first breast first, which really helped me. I had an oversupply and ended up doing one-sided feeding which helped us.
My only other addition would be to hang in there. I KNOW it sucks, but it really does get better over time, as the baby's gut matures.