Do reconsider the possibility that it's reflux.
DS2 had it.
He fed really well (was never off the breast) and I was delighted with him for a while (after struggling to establish bf with DS1).
He did all the screaming after feeding, going rigid and also had so much gas.
He also had a constant cough and snuffly nose.
Originally the gp just gave me gaviscon, but then when we saw the pead (sp?) at 3 months, she laid him down, he coughed, she sat him up, and he was fine, and she immediately diagnosed reflux with damage to the oesophagus
.
She put him on better medicine but I can't say it totally "cured" him.
I watched my SIL struggle with her ff reflux baby, and honestly I can't imagine coping with hearing your baby scream and scream with no way to calm them (ie bf).
It's hard but after about 5 mths things gradually improved although it took him a couple of years to sleep through the night!
In the early days I held him upright or in the baby carrier for a couple of hours after a feed or put him to sleep in his baby chair by my bed (we invested in a good straight backed one).
Later we built a kind of sling with the baby carrier to put him to sleep at 45°.