Levothyroxine Sodium and synthroid

I have taken this Levothyroxine ever since I got Thyroid Cancer in 2006. And thank God I am free from cancer now. My main problem now is that, sometime I really don't know what was wrong with me and get confused over my own feeling. I do have cramps, sleep problem, headache, menstruation problem, mood swing, panic attack and always thinking of a negative thing eg like am I going to die. It has been bothering me since than. Please help I just wanna know is this really due to the medication or its really that I am going to die. I am very confused at times when feeling this side effect. =(

Started taking Levothyroxine 100 3 weeks ago, for last week I'm in agony, my joints and muscles are sore, specially legs and arms, got constant headaches, mood swings, I'm also short of breath which developed before muscle pains, went to the doctor, was told it's probably asthma (!!) got tablets and inhalator and he mentioned anxiety, when muscle pains started, went back, was told that it's not related with hypothyroidism or Levothyroxine, it's a virus (??) have to drink plenty of water and got Diazepam and link to anxiety website. Help, it's not stress related! I don't know what to do!! Does anyone know how to get rid of those pains?