@koronkebitch
Writing can be frustrating, because it is long, tedious, and more importantly, defeating. I think one factor for me is the lack of direction and don't know how to recover if I reached a dead end.
If this is indeed how you are feeling, I think it can be helpful to realize that this is the same frustration as many early researchers. Through time, you have become so familiar with your field and gained many intuitions on how to react in different situations, then research becomes more rewarding.
So just like research, I feel maybe you just need to push through it a bit, go to a coffee shop, library, set a ddl, just force yourself to face the writing. I personally feel that my writing eventually more purposeful after practices, and that makes the process more fun and efficient.
On the other hand, the "the next project" is waiting for you on the other side, which is always exciting. 😉