I think you might be burning yourself out. Space out your gaming sessions a little more, and try turning the difficulty down a notch.That being said, and coming back to Stalker, I've kind of had enough jank with Stalker. So I don't think I'm in the mood right now to even try Call of Prypiat.
Clear Sky I'll probably not even continue, since I watched a few reviews and it was mentioned that this one has constant gunplay, unlike the original. That certainly is not what I appreciated most in the original.
I used to always play on the hardest difficulty too, because I enjoy the challenge, but then I realized that, with most games, it doesn't actually make the game more challenging in any meaningful way, it just makes it tedious. So now I go with whatever the second-hardest difficulty is and usually find that to be a good balance.