When your thyroid isn't functioning up to par it can leave you feeling exhausted, overweight, freezing, depressed, constipated,
brain foggy, and more.
If u want to check whether it is really or not overtraining, more popular are muscles, leg pains
when walking up the stairs (legs like wool, you can not produce the maximum strength), morning heart rate (some more beats if it is 1 or 2 stage of overtraining or less
when advanced), need for salt / carbs,
foggy brain, headaches after more effort / tiring day, disturbed relations with family / friends, sleepiness (everyday) after meals, insomnia, mornings fatigue, or simply — take something heavier and exercise it, and if you'll feel shooting in the joints, weakness of the ligaments and muscles, you can be sure that you are overtrained.