1.its just like really fat, can't swim properly, goes to the top of the tank and like open its mouth I don't know is it because they're is not enough oxygen
2. 1 month or more
I don't know about the other things (ph etc) don't know how to see
3. I had it for like 2 months or 3 it's acting weird since 1 week
Have you got a filter running on/ in the tank?
Can you post a picture of the tank?
Can you post a video of the fish trying to swim and breathing at the surface?
If you can edit what you wrote above, it might help. I don't understand what you wrote for 2 and 3.
Are you aware of the aquarium nitrogen cycle and did you cycle your tank before adding the fish. He looks pretty bad. Do a 75% water change everyday for a week and get an API freshwater test kit to determine your water parameters. This is very important. Get back with us.