Okay...could be anaemia, thyroid, diabetes, something to do with your immune system, a vitamin deficiency, stress, post viral fatigue.....and thats justoff the top of my head.
I have underactive thyroid daffy and doctor has just dropped my thyroxine from 125mcg to 100mcg as she said it was just touching on the high side (what ever that means) and to see how I feel for the next couple of months but apart from that and some arthritis I have no other health problems
Just a guess, mind you, just an outside guess, if by the "high side" she means your blood TSH levels are high, then you should have increased your thyroxine dose and not decreased it.
Find out when you see your GP what the level of TSH was and get back to us.
The symptoms you are having are probably due to your medication dosage being reduced. If they don't settle you will probably need to be returned to the higher dosage. I would ask the doctor about it sooner than 'within a couple of months' though if it were me.