I have been on Synthroid for years for hypothyroidism. All of the sudden my levels have gone crazy. I felt my muscles burning do the simplest tasks, major fatigue, problem swallowing, and hair thinning. I contacted my doctor and we did blood work. My level was up to 9.92. The doctor game me an addition 50 mcg which totaled 200 mcg now I was on. After a couple of weeks of that, the symptoms were getting worse. I went back and we did more blood work. My level had risen to 12.29 and my thyroidglobulin level was 333. What on earth would cause that??