Did past dieting damage my metabolism?
Not necessarily. Restricting your calorie intake over a long period will slow down your metabolism rate (the rate at which you burn in the body) and there are two steps to increasing your metabolism:
First, increase your activity level, which will boost your metabolism rate, especially if you combine strength training with cardiovascular strengthening exercises. Resistance training helps build muscle and is more metabolically active than fats, but it should be clear that fats are an important nutrient in any balanced diet.
Second: Start gradually changing your eating habits. Increase food intake to coincide with your higher activity. If you balance what you eat in protein, fats and carbs with what you burn, you will reduce the likelihood of gaining weight.