Thryroid cancer symptoms and conditions

I have been taking Levoxyl for approx. 5 years following having a total ablation of my thyroid due to follicular thyroid cancer. I am constantly tired, have joint pain, trouble sleeping and continue to experience weight gain. The doctor continues to tell me this is not from the medicine and to improve my diet. My vision has also gotten terrible over the past two years. Has anyone else experienced this and do you know of anything that helps?