My son (27 months) had severe acid reflux in infancy and started on meds at 2 months. It still hasn't resolved itself but it is a pretty severe case. He also has a very happy disposition and things like reflux, teething, and ear infections have always revealed themselves more at night than day. The symptoms do sound very typical to me, although I agree that 7 months may be an odd time for it to suddenly come on. Some reflux kids spit up, some don't, some avoid food, some (like my son) use food/milk as a soother for the burning. We also had him sleep in his car seat and then we raised the head of his crib (with thick books) for many, many months. We also had many struggles with medication dosages. I've heard that reflux and some allergies (like dairy) can be confused. The only way to really confirm infant reflux is an upper GI (which my son had at four months). However, if symptoms resolve after starting meds like zantac or a proton-pump inhibitor like prilosec or prevacid, you pretty much have your answer. These drugs do take away stomach acid though so they are not to be taken lightly.
I recommend a couple of websites:
we have a pediatric gastroenterologist at MN Gastroenterology in St. Paul, their website has some patient education: www.mngastro.com
www.infantrefluxdisease.com was a big resource for me when my son was little and has a ton of info - I caution you on this website though because the information is gathered more from advocates and experienced parents rather than doctors. The basic stuff is pretty reliable but some of the guessing that people do linking reflux with other issues may not be scientifically based - the message boards are outstanding.
I can understand why you think it might be teething - it's just that the arching of the back and not wanting to be flat are telltale signs to me of reflux or something digestive. Good luck and follow your instincts!