problems stomach /carbs after few hours

I'm training and recently finished a few ultra trailruns (100M). After 8 hours everytime I have problems with eating and for the rest of the race it is a horror.
What happens is that I have the feeling that I have to vomit and sometimes I have to vomit but nothing leaves the stomach.
After 8 hours, when I put an energy bar/banana in my mouth, the vomitting reflex starts. The end result is that my energy goes away from lack of carbs in my body until the end of the race.

I already went to a doctor. 2 days previous the race I eat every day about 1000g carbs. With the carboloading I don't have any problems. No vomiting reflex.
During the training I eat about 75 gr every hour, also no problems (I train maximum 8 hours in one day).

I also train with different brands of bars/ drinks to get used to the different types.

Does anyone have experience with this problem or has a solution?