I have been using Eltroxin for 6 years and test my thyroid regularly My thyroid was tested on the 8th of Jan 2010. My doctor decreased my medication after telling me that my thyroid is slighty under active. My TSH reading was 5.16 [norm 0.2-4.5]. I tested again on 15th Feb 2010. The TSH increased to 21.64. What medication should I take ??