Have you had your thyroid numbers checked since your surgery? Surgery and healing are very stressful and can mess with your body's needs.
I don't know if it's the same type of situation since you had yours removed, but I'll tell you what happened to me. My thyroid was slowly going downhill, but still fairly normal, but then I had ankle surgery and it sent it over the edge and I required medication. I was doing great on my dose until I had another surgery, and then my symptoms came back again and I had to up my dose, been doing fine ever since. So it seems that surgery doesn't work well with my thyroid.