How to find your way in this game

Hey, I now have around 150h in this game and I can't find my class and especially weapon. Somedays I'm solid with a 2:1 KD, placed in the middle of each round. Then there are somedays like today where I have the feeling to loose every gunfight and barely leave a match with a positive KD.

But most of all my gun analysis paralysis sucks. I always think I'm using the wrong gun. I keep switching guns all the time and can't stick to one (although I know I should).

What's your advice? Do you experience sometihng similar?