Your missing a lot of key facts. Like how tall you are, bodyfat percentage, ow often you exercise, was it a general practitioner doctor or was it a doctor specializing in weight loss? A general practitioner is good if your sick or have something weird come up you want looked at. If you have a genuine problem in a specific area, it is time to see a specialist.
Your city also matters because if your fatter then what is normal for your age group then that is cause for definite action. If your middle of the road then you might need to see another kind of doctor entirely.
The first things that would come to mind are medical issues, such as thyroid, insulin resistance, PCOS, etc. These will all cause weight gain and/or prevent weight loss.
You said you had your thyroid tested and there were no problems. I'd have to see the actual lab results, with their reference ranges, before I'd agree totally. Many times, a doctor will only test TSH, for thyroid, and if it comes back in the "normal range", they say you are "fine". That's not true, because TSH is a pituitary hormone and not the best indicator of thyroid issues. There are many other tests that can/should be done before thyroid is ruled out completely. I'd recommend that you check out the thyroid forum here on MH - there's great information there. You can also send me a PM for more information.
Additionally, insulin resistance can also cause weight gain and/or inability to lose. Many times, thyroid issues, insulin resistance and PCOS go hand in hand, so you should get checked thoroughly for them all.
That said, I don't know how much weight you are trying to lose, what types of diets and exercise you have tried. Eating healthier is not really ALL that needs to be done. You need to watch the number of calories taken in, versus the number of calories being used, as well. The type of exercise is also important; you need a good mix of cardio and strength to get overall benefit.
If you can tell us your height and give us an idea of what you have been doing to lose weight, maybe we can help you come up with a plan that you can stick to.