Hoan Ta, I just watched your videos after the first month and the second month. I would suggest going back to watch the first video and compare it with the second video. What differences do you see? For each difference that you see, is it a positive or a negative change? Often what happens when one tries to correct one problem is that other problems creep in because we are not concentrating on them. There are two challenges to learning good swimming. First one must learn to see the mistakes one is making, and second one must be able to correct them without new ones creeping in at the same time.
Good Luck! You look very impressive after so short a time practicing.