how much exercise would i have to do?

depends what kind of exercise you do and what you eat

I don't think it's possible to know, it depends on how much your planning on eating for a start. If you eat tons and tons and exercise loads you'd probably stay the same would you not? when I'm dancing everyday I eat tons and don't lose weight (I just stay the same). I think in order to lose weight especially if you don't weigh that much you have to go hungry. If you exercise a lot you burn cals and are hungry and so you eat more than normal anyway (well I do). You'll have to exercise more and eat the same as before to lose weight I should think.

Consult your doctor.

Its quite simple really, you have to burn off more calories than you consume to lose weight. Try and add up how many calories you eat in your average day. To lose weight you need to exceed this amount in calories burned. Obviousley, you dont need to burn off all the calories you consume, you need some for basic energy, think its around 2000 a day for a female. Bear in mind that to lose one pound you need to either cut down you intake by 3500 calories, or burn off an extra 3500.

1500-1700 is fine,its within daily guidelines.could you cut it down to 1300/1400? even if its just a few days a week on lower cals? To lose a pound a week you need to burn off 3500 on top of you 1700, if you cut down to 1300 you wouldnt have to burn off as many. do you have some kind of monitor to check how muich you actually burn off at gym?

Ask one of the personal trainers at the gym?

That is really inaccurate.

Im just saying what i have been told at weightwatchers and other places!

Of course you burn off calories by just existing, but to lose a pound of weight, your intake of calories needs to be 3500 less that what you are burning off through 'existing' and through exercise. You can either eat less or move more!

And an hour of excercise will change your calories, i burn off 500 in an hour at the gym.

Weightwatchers = bull****. Its marketing is focused on cynically exploiting middle aged women who want to lose weight. Sorry, it's a stereotype, but it's true. Ultimately, calorie counting is a rather useless pursuit. Losing too much weight too quickly is very unhealthy and is likely to lead to muscles as well as fat being burnt off. The best way to get fit is to exercise hard, and then eat a lot, which is what the OP seems to be doing.

Incidentally, what tell you that you're burning off 500 calories - the running machine? Don't believe it.