The limit of earning qi in a day is 100, that means you maybe reached the qi limit of earning in a day, come back tomorrow, and that will get your qi raise up again.
It could be a number of problems. You are probably completing games too quickly. This has happened to me also. If you are playing a mod which -Ze- is referring to, then QI will not add on. For further questions I can send you to this Link.
Just message an admin if none of the suggestions worked.