I have gained 30 pounds this past year. i always watch what i eat and try to exercise regularly. just had thyroid test and result were normal. age 39?

Balance: After ruling out and normalizing metabolic factors related to weight gain (thyroid, Insulin resistance, etc.) creating a calorie imbalance towards burning more calories than you take in will generate weight loss. It takes approximately 8000kcal to burn 1 kg. The regulation of weight is very complex hormonally. Many have proposed a hormonal basis for various diets but the data is limited.

Eat less?: Assuming your thyroid is normal and there are no other extenuating circumstances, the most likely thing is that you're eating more than you think you are. Sit down with a qualified registered dietitian or consider q quality program such as weight watchers. Counseling may also be of help. Good luck.