A seemingly Norse boy who is ugly and killed a man in revenge

So the general plot that I can remember, although my memory may be faulty, is as follows. A boy who was born in winter, he is very ugly and many times throughout the book he is described as "Frog looking". It seems vaguely Norse, like an old, a very old setting, with many different groups that work together but are distinct like tribes. So the story really kicks off when a bunch of these tribes are invited to this boys home for a meeting of some sort. The boy meets one of the other tribes daughters in an orchard they have a striking meeting but she is mostly irrelevant for what I can remember of the rest of the story. Then, when one of the "chiefs" of the other tribes is with the boys very drunk uncle in the stables, the uncle ends up being killed while the boy watches and the "chief" rides away on his horse. The boy then goes on a journey without telling any of his family, to go and avenge his uncle's death. I remember he seems to have met an old man merchant on the road who was a trickster of some sort and I think the boy may have murdered him or hurt him and robbed him, something along those lines, anyway they have a negative encounter. When finally the boy gets to the little town that the "chief" lives in he sneaks in, because he is very distinct looking (frog-looking), he sneaks in through the gate past the guards. He gets to the "chiefs" house/castle/manor and it seems the man had caught an illness that left him horribly bed ridden and looking of death. The boy is briefly conflicted about killing a sick man, but he exchanges a few words with the man and when the man's son somehow becomes involved in the encounter, I assume defending his father, the boy messes with the fireplace and the house burns down on top of the man. When the boy returns to his home there is another meeting of the tribes, they are trying the boy for murder, or trying too, although there is no concrete proof only vague descriptions of someone "frog-looking". His mother then lies to the council and says that for the past month, or however long he was gone for, the boy had been at home helping with the planting.