IFN can aggravate thyroid disease. Can cause hypothyroidism or hyperthyroidism -- thought due to activating immune system attacks on the thyroid. Close monitoring is important. Would check levels off levothyroxine at this time to see what the thyroid is doing on its own -- if hyper, treatment may be indicated especially given the symptoms you have. It is not something to "not worry about".
If your Dr. told you not to worry about being hyper I would find a new Dr. Hyperthyroid, specifically Graves disease needs to be treated. There are many, many symptoms that one can have when they are hyper. I have recently been diagnosed with Graves, my only symptom was my heart racing (resting rate 110- bpm). My Dr. really scared me about not taking paying attention to the problem and put me on beta blockers immediately. He got me an appointment to see an endo doc as I was standing there in his office. Call you family dr immediately and explain to them symptoms, they should see you ASAP.
Good luck and hope you feel better.