I eat 1400-1600 calories a day and i do cardio for 40min 4-5 days a week. i am getting bigger and bigger. i don't fit in any of my pants anymore. why?

Need less calories: You are likely eating more than 1600 calories per day or you have a very slow metabolism. Basically, if you are gaining weight, you are taking in more calories than you are burning. To hold your own or to lose weight, you need to burn more calories with more exercise or consume fewer calories. A well balanced , healthy diet and regular exercise are the keys! good luck!