I have to concur it was the dogs. My low stamina high strength knight certainly had problems evading and disposing of them quick enough at the first few tries, but I did kill him eventually.
Ornstein and Smough were not too hard, took me three tries (1st one I died, second one I let myself being summoned, and on the third try, I summoned two helpers and killed them with relative ease).
If any boss is too troubling, that was basically what I did do: let myself be summoned until I learned what to do, then, depending on how difficult I found the boss to be, recruiting a little help in addition to the knowledge.