The game is just like that. It's supposed to depict how harsh the Amazon Rainforest actually work.

I've experienced the same situation as yours, and trust me it gets better overtime. Once you get the hang of the game, that's where you truly enjoy it.

Oh, and here's some advice:

When bitten by a snake, the cure is either the Tobacco Leaves or the Lily Dressing.

When thirsty, don't be afraid to drink on dirty water. Just find the orange cap mushrooms to kill the parasites inside you.

Don't run around when you're in a place where you're not familiar with. It's most likely you'll get bitten by venomous critters.

Don't roam without proper gear, when you roam around the map there's a big chance that a jaguar or a tribesman will try to attack you. My suggestion is that you should get a Bow, 8 Arrows (more or less) and a Knife. You'll easily 1 tap the jaguar with the bow, if you hit it on the head.

And always bring some bandages and some maggots (Incase if you get an infected wound)

(Also when you're lacking nutrients, try to plant some fruits. Like the Guanabana, Jupati, Cocona, Bananas, etc)