regain

I don't know how to keep the weight off!

It always creeps back on little by little even when I am exercising!

My weight problems are up and down constantly!

Which leads me to ask, what can I do if exercise all of a sudden is'nt enough?

It use to be.  Do I have to be a slave to the gym??

Is there a diet plan that I could stay on for as long as I need to, that will help keep me slim?

   Thanks.

Maintenance is a balance between energy going in (food) and energy going out (activity).  If you're at a natural healthy weight you should be able to stay within 3 or 4lbs of it by eating a reasonable amount of good foods and by being reasonably active.  By 'reasonable' I mean that you should be able to get circa 2000 cals a day (depending on your size/age) and be active for half an hour a day, give or take.

If you can only maintain your weight on a very restricted diet and/or with large amounts of exercise it could be that the weight you're trying to maintain is unnaturally low.   Either that or, if you've been dieting for a long time, you could be experiencing a problem a lot of long-term dieters find which is that their bodies start to get used to lower calories... making weight-loss more difficult and weight-gain a lot easier.