Definitely do more cardio... but do different kinds of cardio (and for at least 5-6 days a week at least until you get over the plateau)!
Like for instance, if you were running beforehand-- do circuit training, stair master, jumping on a mini-trampoline, spinning classes, kickboxing, etc.
Also, incorporate weight lifting into your routine.
And calorie cycle on occasion. All those things will definitely bust your plateau!
Hang in there!
~ tea