Hello, Chills are non-specific symptoms that may come from several different reasons. However, one of the likely common causes is a thyroid condition. The fact that you were recently diagnosed with hypothyroidism and is on a high dose of thyroid medication which I suspect your initial thyroid level was significantly low. I advise you to repeat the thyroid function again to ensure the current dose is adequate. Cold intolerance is one of the most common symptoms from hypothyroidism, so this is likely cause that may be contributing to your current symptoms. Severe hypothyroidism can also cause symptoms such as signs of hypothermia. Again, it may be mixed presentation because mono virus which you mentioned above can also cause chills or it may be other causes such as another viral disease like influenza that you may have caught. Please follow up with your primary care doctor or a doctor who is managing your thyroid condition to make sure your current dose is adequate and discuss further on any testing if indicated. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Katie Lee, General & Family Physician