Stomach pain training advice

I’ve been training fairly consistently for 8-10 months 3-4xs a week. Before every class I get some nerves and as soon as the class starts and my heart rate gets going I feel my stomach start to cramp up and hurt.

I don’t eat after 12pm (my class is at 6pm) out of fear of throwing up.

Does anyone have any advice on what to do or take in order to ease my stomach aches or prepare physically for class? Stupid question I know but it’s really frustrating dealing with it every time I train.

Thanks in advance