I'm not aware of any food increasing the blood recovery rate (lingonberries and liver might help a little in real life as they're rich in iron, but I don't think lingonberries have any such effect in UrW).
When my characters have suffered significant blood loss I won't touch the wounds until the blood has recovered, and when starting to treat the wounds again I'd keep blood staunching herbs/blends at the ready.
I doubt UrW actually takes activity level into account. You may try taking sauna baths as they may or may not help (they shouldn't be harmful, anyway, and are certainly the right thing to do from an RP perspective).
And, by the way, how do you manage to get an unfortunate encounter with 4 Njerp warriors? The escaped slave scenario has a war camp, but if you actually managed to flee, you should know it's there. You can also attack Njerp villages (or pass near them, to get attacked), but again, you see the village at a distance.
The third option is that you've managed to find a Njerp war camp that isn't tied to the starting scenario, which would be exciting, as I'm not aware of anyone having found any of these (although they should exist, if I've understood Sami correctly).