I do not have thyroid problems but I do have many patients with hypo or hyperthyroid problems. Both spectrum can cause loss of concentration, forgetfulness, "foggy brain". Make sure your enzyme levels are within normal limit. Otherwise, you may have to adjust levothyroxine/synthroid that you are taking.

But people still do have foggy brain once in a while although you are taking optimal dose. I am not sure how long you have this issue. A lot of people tolerate better with time.