Sounds alot like reflux symptoms that my DS had... he didn't vomit, but had silent reflux and the back arching is a dead give away I am told. DS was diagnosed at 5 weeks after a terrible fortnight of sleepless days and nights and screaming at every feed, and extended feeding times.

Talk to your paed or GP, don't take no for an answer if you think there is something to it. Our Dr was a lifesaver. DS was on Losec and later zoton. Both worked a treat.

It is tough. Good luck. Hang in there