I can't remember what I had as DPS at that level, but it seems a bit low. I would say upgrade to a bow with a nice quiver for the bonus, and search out some gear with vitality and dexterity to help out.
If you stay with the curve of gear through normal and NM, every opponent is pretty laughable. Upgrade!
I had a hard ttime at first yesterday on my DH too, about the same level. Died twice then figured it out. Obviously, avoid the green spots because those are where he's about to hit. When he does the attackk where it seems everywhere has a green spot I ran from one side of the room to the other, hugging the guardrail and I didn't get hit. After I figured that out it was a piece'o'cake.
DPS seems fine for normal, you just need a bit more HP. Anything under 1000 will have a very hard time, while anything over 2000 will have it pretty easy. Aim for somewhere in the middle, would be my advice.
With 55 Vit, your HP is probably under 750. Belial's giant fist can alone do 300-400 to a character like you, and while it is possible it's not likely you'll be able to dodge EVERY single one. Look for VIT boosting gear to get your HP to around 1500. Your damage is actually too good, but your survivability is on the other end.
I consider having 90-100ish damage when fighting Belial to be standard.
The rule in this game is if you are having insane problems doing crap then you gear is wack. Dps is really low as well, needs to be at least 500+. So dont be a queer go to the Auction House and get yourself some better gear. If not then Lord Diablo will have fun feasting on your soul in hell.