Ok, there are a lot of reasons why you have weight plateau but here are the most common:
1) Something wrong with your nutrition.
2) You are overtrained. Doing too much cardio, workout every day and cut your carbs to 0 - and you will stop losing weight very quickly. Moreover, you can even gain some extra fat. Give your body and brain a little break if you workout too much/too hard.
3) Not enough sleep
4) Too much cardio