There are so many factors that could be contributing to this. You could be eating to many simple sugars, not drinking enough water, eating too much sodium, not eating enough.

Remember when it comes to your exercise, that it is your bodies main goal to do the exercises that you do on a regular basis with the least amount of energy expenditure that it can, which also means the least amount of calories burnt. That is how your body becomes efficient. When it come to weight loss you want your body to stay inefficient because that means your still burning high calories and getting the most from your workouts. try not to just stick to cardio as well, make sure you're challenging your body by strength training and maybe throw a little bit of interval training in there to really give it a boost.

Good luck and feel free to add me if you want

Edited to say: Also when training with weights, dont be afraid to pick up some heavy weights. it'll do your body more good than you can imagine. You will not get 'big'. you will not get 'bulky'. you will get toned lean muscle mass and it will look stunning