The more I practise, the more critical I become and I'm starting to lose confidence

[Mrbigstuff]

If you’re practicing to improve it’s not always going to be fun. If it’s a tricky passage then playing it slowly and repeating while speeding up can be tedious. Learning theory and practicing scales up and down the neck isn’t always musical. Sight reading practice can be fun if you get a good tune but to be effective it should be something you wouldn’t listen to or from an exercise book. 
The point being, practice inherently won’t always be fun if you’re doing it right, but when you get it all together and your performances improve, it is worthwhile.