What is thyrotoxicosis? Please answer?

I have an under active thyroid and i've been taking levothyroxine for a year but it doesn't get rid of any of my symptoms. I also have adrenal fatigue. But one doctor i saw said that i was thyrotoxic because i had so much T4 in my body which was unusable. Surely if that was the case, i would have symptoms of an over active thyroid? All my symptoms are under active symptoms.