You fought a White Dragon at what level?! Ummm... Are you sure your DM has a Monstrous Manual and actually knows what he's doing? I mean, that just doesn't seem right, not to mention that it was a random encounter. Maybe you oughta have a talk with him about what you're encountering unless everybody else is ok with it. He kinda sounds like he's inexperienced from the little I can learn from what you said. Like a lot of other people said, maybe you should find another group to play with or at least get a new DM or something... Asking if you could go on a couple solo adventures like somebody also said would probably help to. Just my 2 cents
-Jafin