I've been preparing for CAT since May but score in Mock test isn't consistent.

Work hard and do more practice on the questions you are not able to solve. Just giving mock tests will not work,  rather try to improvise upon the area you are lacking.

Don't get demotivated with low percentile in mock tests. Give test without thinking about percentile. Don't deviate from your aim which is to maximise the questions to be attempted with accuracy.

All the best!

Fristly, scores in mocks are dependent upon number of people giving that mock, and its not comparable. Initially good mock score canbe because less number of people appear for mocks and now everyone starts appearing. I would suggest evaluate your each mock test, questions where u marked wrong option and how can u improve your speed. Percentile would improve automatically