Issues with my thyroid?

I'm 14 years old and I think I have an overactive thyroid that is causing me to gain weight. Last year I was diagnosed with Hyperhidrosis, a disorder where you have overactive sweat glands. In other words, I would be sitting there with sweat just dripping off my hands. I have had this issue since I was a toddler and have also had more weight than is healthy despite 3km of swimming training everyday and a healthy diet. At first I thought it might just be hereditary, but after numerous attempts to get rid of my Hidrosis, a doctor suggested that it might be my thyroid. After thinking about it, I realised that metabolism and weight gain can be affected by the thyroid and hence my current theory: An overactive thyroid is making me gain weight and also causing my hidrosis.