When you defeat the first boss (Eikthyr) you get several antlers. Three iirc.

Are you saying that you were carrying all 3, died in a river and now can't retrieve your gear? OR was it only 1 you lost and the others either need to be made or repaired?

I'm guessing here that you drowned in the river and weren't killed by mobs. Your death marker will float so maybe go to the river and then eat 3 types of food that give you the most stamina. Raspberries, red mushrooms and deer meat maybe? Make sure you have plenty of room in your inventory and retrieve your gear.

I don't know if this still works but logging out and back into the game used to return you with full stamina. So you could test that and if you're still running out of stamina with good food you could log out and in.

My tip (for this early in the game) is don't take all your pickaxes with you. You can't carry a lot of ore and using up 1 pickaxe will likely get you fully loaded.