Hi OP,
I’m sorry to hear that you are not having fun. I agree that it can be frustrating sometimes to have to learn everything from scratch in a new expansion, especially if you like playing multiple classes.
However, if everything stayed the same I feel like I would get bored too quickly. I think that the reason I have played since BC is that it feels like a new game every few years, but with the same characters and overall world to link everything together.