It's impossible to determine if the cause of your hypo is from autoimmune thyroid disease just by looking at FT3, FT4 and TSH. However, since Hashimoto's thyroiditis (autoimmune hypo) is the most prevalent cause of hypo in the developed world, it's a pretty good guess, and I think that's exactly what your doctor was doing. To confirm Hashi's, ask to have TPOab (thyroid peroxidase antibodies) and TGab (thyroglobulin antibodies) tested. They are the markers for Hashi's, and both must be tested before Hashi's can be ruled out.
Please post your lab history (recent) and include reference ranges. Ranges vary lab to lab, so they have to come from your own lab report.
Are you on thyroid meds?
Your thyroid levels can change from just about anything! Stress, food, medication, etc.
I've dealt with this for years. My thruroid tsh level is currently close to 300. I take 300mg of synthroid a day. Lately I've been under a lot of stress and my levels have gone crazy. I feel your pain, my body hurts and I feel horrible. I was hospitalized last August because my TSH reached 500.00. You need to be careful and keep a close eye on ALL your levels. I had synthroid given through IV then was taking 1200 mg of synthroid monitored by Drs. This is nothing to play around with. I was out of work on Medicaid for many months, couldn't drive, walk etc. please be cautious. If your aren't feeling right remember you know your body better than anyone else.