Because you do have the symptoms of thyroid, wether hypo or hyper.
It is similar symptoms of a diabetic.
I could go on and on a very long post about why carbs are bad for you, but it would be easier for me to refer you to the low carb forum. There you can pick and choose what to read and what to believe.
There is an undercurrent of new thinking that carb overloading for competitive sports people, is causing problems later in life. With thyroid and type 2 and recently RH becoming more prevalent with ex university trained athletes in all sports but especially long distance endurance sports.
Is there any particular reason why you have opted to post in the reactive hypoglycaemia forum? Or did you mean to just put the post on the open forum?
Last word, doing low carb correctly will increase your energy levels and the tiredness if your condition is controlled, you should feel better and your training and competitiveness should improve. The carbs do affect your imbalance created by your thyroid.