You need to find out what's wrong, don't be afraid of going to the doctor. Treatment could be extremely simple anyway. You absolutely cannot get a diagnosis over the internet so please just make an appointment with a blood test. That's all that's needed to diagnose or rule out hyperthyroidism. Two important symptoms are weight loss with no cause and feeling hot, your GP probably will ask about weight. Not that having no weight change excludes you but it does present in a lot of people. I myself am hypo, but I am underweight despite the major symptom being weight gain. You gain nothing from sitting at home worrying, make that appointment! Nothing to be afraid of, just walk in say you want a thyroid blood test and explain your symptoms. Your GP may want to carry out other blood tests also and may forumate a few routes to go down if the thyroid test comes back negative. They're pretty fast, results should be back in under a week.