Your story sounds very much like mine. My DD started the screaming when I was still in hosp too and the midwives couldnt settle her either. I recommend getting her started on the losec ASAP. My paed mucked around and put my dd on zantac at 3 weeks which did nothing, he never listened to me about how bad it was. I researched and demanded losec so she started on that at 4 months. It helped alot, though never fully stopped the pain, but compared to how it was it was a miracle. Try and get onto meds asap as this would have helped me DD not have other probs associated with it, like pain association with feeding, unable to isolate muscles, and super tight muscles from all the back arching etc - We ended up having to see a physio for months.
gluck, I know how upsetting it is seeing your child in pain when you feel like you can't do anything to help. Watch out for yourself too, I developed PND, which was because of how sleep deprived and hopeless I felt about the whole situation.
My DD is almost 19 months now and is still on losec, but most babies are off meds by 6-12 months.