underactive thyroid
"I've been on Levothroxine for about 8 months now, with vaying degrees of success. 

My doctor told me it was becasue it wasn't absorbing properly.  You MUST take it on a completely empty stomach.  In the morning after 8-10 hrs of fasting.  If you follow this rule you will find the drug works as it''s supposed to.  It changed for me and I lost the weight I had gained."