why am i not losing weight?

i am SOOO frustrated! i do not understand why i am gaining weight rather than losing it.

i eat around 1000-1200 calories a day [healthy food- no processed or packaged food, sweets, or high carb breads], do a light weight training workout for 15 mins and do at least 30 mins of cardio.

in the past 3 weeks i have gained weight! i don't have a scale or anything but my pants are tighter and i can tell that ive gained weight by looking at my figure. it drives me crazy because swim season is coming fast and being a teenage girl, i am expected to look slim and fit!

it seems like the only way i can stay slim is to eat like nothing but i dont want to do that so ive just been trying to eat healthy and work out.

does anyone have any advice or suggestions to why this is happening and what i can do to fix it?

Definitely need more information.

How tall are you?

What is your current weight?

Age?

What is your predicted RMR/BMR?

How much weight have you gained?

What does your diet consist of?

What does your aerobic and anaerobic training consist of?

Have you been measuring your weight at the same time each day? (i.e. in the morning as soon as you wake up)

Have you been properly measuring and monitoring your body fat percentage and lean body mass?

People tend to focus too much on scale weight and completely ignore their actual body fat percentage.  When coupling regular aerobic exercise with anaerobic exercise, you WILL gain lean muscle mass (assuming proper execution, diet, and rest).  You will in turn reduce body fat percentage, as muscle burns fat.  However you may maintain the same scale weight or even GAIN weight due to the increased lean muscle mass.  The goal shouldn't be to reduce scale weight but to reduce body fat percentage while increasing lean muscle mass.

Your body is probably in starvation mode and holding on to every little thing you eat. You are WAY under calories. You should be eating at least 1200 calories, and if you are exercising you need to eat more. There are tons of posts about this on this website, but what you are doing is not healthy, you are starving your body.

This is a common question, and sparkler is correct.  What most people seem to not know about dieting is that if you go under a certain amount of calories, you trigger "starvation mode" which is where your body holds on to fat instead of burns it.   I did not know this, which is why my first couple of diets were total failures.  I ate too little!

If you use the "allowance/expenditure" tool on this site, it will let you know how many calories you should be eating.

Try doing a heavier weight work out.  I spend an hour at the gym lifting weights and do maybe 20 mins of cardio 3 days a week and do two 45 min cardio classes the other two days.  Lifting weights makes your metabolism faster.  I've noticed a big difference in the last month, Nothing major, but my budah belly is starting to tighten up.

This may answer some questions http://www.bodybuilding.com/fun/core_march_8. htm

BG

 thanks soo much you guys! i think i finally understand this. im not losing the weight even though i eat healthy food and work out b/c my body is in starvation mode. even though im not hungry [its b/c my body is used to lower calories], and i need to eat about 300 more to lose the weight!

thanks very much to bgerding2.. that article really helped!

if anyone else has more advice it is greatly appreciated!