I've put some of my own insights and also some questions in the sgf.
I think it also happens to some people. But yeah, I suddenly feel like I don't know what I'm doing or where to play anymore. Well, somehow my reading is still ok-ish since I can still do some tsumego stuff on phone. But my theory has gone to oblivion (or something like that) lol... 
Btw, I'm around 1d-3k at worst. I have a 2d tygem (just made it 2d from 1d) and a wbaduk 2d and 9k (from 21k made to 9k so far and too many games needed lol)
I hope some dans can enlighten me. It's really so hard when you have to study all by yourself, you wouldn't know if what you're doing is right or where to improve... but I hardly know any dans personally that's why I tried posting here... I hope it's not a waste of your time to help and I thank you all in advance
how about C3 directly ? Why do you feel the need to push here ?
since W backs up, I wonder if you should push one more.
in the diagram below) and connects D5 instead? If White goes ahead and connects at 
to cut, Black will cut in turn at 
. Although White can atari at 
and capture 4 stones with 
, Black ends up with a very big corner and White's shape is over-concentrated. If White approaches the bottom right corner now, Black will not pincer but rather attach underneath and happily take a second corner. 
This misses a big chance, I think. Play at K2 and the white group to the left is going to have to run out. Since White already has a weak group on the left side, you should be in good shape for a strategy. If you play the pincer, you have to think in these terms.