this is not working for me

Then you are netting 900 - 1100 calories and that probably isn't enough. You should try eating more.

If you're doing the MFP method, you're supposed to eat back exercise calories. MFP is a NEAT method calculator, not a TDEE method calculator. If you're not eating back exercise calories, your net calories are way too low and your body is just storing rather than burning because it thinks you're in some kind of famine or something.

im 5'5 143 lb. 25 years old. eating 1400 - 1500. burning from 300 to 500 everyday and not losing weight or sometimes i feel im gaining. pls help im so frustrated

There could be a few places where you are going wrong.

1. You are eating 2000 calories (which = 1500 NET) because you are burning 500 calories during your workout. It could be you are not really burning 500 calories .... MFP & many machines exagerate calorie burns. In this case you need to eat LESS

2. You are eating 1500 calories & burning 500 (which = 1000 NET) ..... this would be enough calories for someone who is 4'7" not 5"5". In this case you need to eat MORE

Figure out your BMR ...... calories needed if you were in a coma. Do NOT eat below this number: http://www.fitnessfrog.com/calculators/bmr-calculator.html

Hmmm, what do you mean it "feels like" you're gaining? Have you? Have your measurements changed?