I would check for two things, mites, and egg binding. Egg bound females spend alot of time in the water and may even lay the eggs there, the back arching sounds like a female struggling with eggs, but could just be a pain response to some other problem. Mites can cause waterdragons to spend alot of time in the water and to make wierd movements as they try to rid themselves of them, check around the eyes for little red/black or white spots.