Like most things in Valheim it's just the learning curve. Your first trip to the swamps is a brutal hardcore survival experience. Your second trip to the swamps in a new game will have you thinking they nerfed it into the ground.

Tips for swamps:

Turnip seeds, sooner rather than later.

Root armor. It's light, it has poison and pierce resist on it, and it directly counters all the really nasty swamp stuff except abominations. Seriously it's just super good, I still put it back on when I go back to swamps. Remember rule of thumb for mitigation is shield > resists > armor.

Suggested upgrade priority is cauldron > shield (to level 3) > weapons > iron armor. I know I just raved about root armor but you still want a heavy set for Bonemass.

Abominations are slow and get stuck on everything. Use the terrain to your advantage. Use a sword. After you get an iron shield and swamp food you can parry them. You can try with a bronze buckler, serpent stew and 2 black forest HP foods but I wouldn't. Their attacks are super telegraphed and quite easy to avoid by dodge rolling. Don't use a mace or a spear or a bow, swamps is where enemy resistances become important.

Don't go out at night when you're still in Black Forest gear

Put portals on top of crypts. Only wraiths can reach you up there.

Learn how stagger works if you don't already.

Go slow and be careful while you're undergeared. Spawners will wreck your face if you just yolo into them, usually it's 2 corpse piles and 1 bone pile. If you're having a really tough time you can snipe them from range with a bow but it takes a while and lot of arrows.

Keep poison resist up 100% of the time if you're not using root armor, but I think you're doing that already.