What causes fatigue, insomnia and weight gain while on Levothyroxine?

Hi! I am Abby i have been using Levothyroxin before having the surgery to remove a goiter way back 2003 then took it for 1 year then it was stopped by my endocrinologist. For the past year i started to feel the symptoms i felt before the surgery. My family doctor always telling me that my blood reports are normal that my thyroid is working well but i don t feel that way. It is hard for me to focus & concentrate ,i feel tired always,cant sleep well, its hard for me to loss weight. I wonder if my thyroid has something to do about it?