there is a few tests for reflux but they are apparently quite invasive so drs tend to prescribe gaviscon first off and, if it makes any difference at all, then agree that there is a reflux issue.
my baby is 14 weeks and has been refluxy from day one, with very similar symptoms ie arching back, vomiting and apparently lots of wind with it.
the gaviscon did make a difference to his pained crying and vomiting ut created a whole additional set of problems with trapped wind and constipation, meaning he refused to eat at all for a night.
in the end we cut back on the gaviscon dosage (from half a packet every other feed to once a day) and decided to visit a cranial osteopath. Our GP said she would refer us to a paediactrician if we wanted a prescription for the other, more serious drugs, but as they arent licensed for babies in the UK, she was reluctant to do it herself. It appears that this is really common with most GPs, especially if your baby isnt vomiting so much that they are losing weight.
The CO is brilliant and has made a real difference.
other thoughts - try holding your baby facing away from you, on his front with your hands supporting his tummy, at a 30degree ish angle. hard to describe, but almost like he's like a plane taking off from standing on your lap. it was the only position i could get mine to stop crying in. and is a good one to stop the projectile vomit hitting you .
also, mine only sleeps on his tummy. and the dummy was brilliant - apparently it helps them minimise the tummy pain somehow
good luck