have you checked your blood sugars in the afternoon? IF so, what are they when you are feeling so poorly?
Typically, it is due to a fluctuation of your BS. And usually it is lower not higher.
Keep an exact record of your BS every day for 1-2 weeks. Check it
2 hour after lunch or when symptoms start
and at bedtime.
Then take this record to the endocrinologist. Also keep track of diet and make notations about how you feel.
It would be great if you have the ability to take your blood pressure and pulse rate as well.
Other things to check will be Vitamin D level. This can contribute if it is low but would not think that it would only be in the afternoon.
I am running to a meeting but will check back in 1/2 hour if you need further clarification.