I think the main thing that the OP may be experiencing is run-of-the mill heartburn/reflux. The human digestive system is largely "gravity fed" and designed to work while in a vertical position - sitting or standing. While diving we're largely horizontal, which can cause some people stomach problems.
New divers, however have it even worse. Inexperienced divers tend to spend ALL of their time cycling between being horizontal, head-down, horizontal, head-up, horizontal, head down, etc... while also leaning to the left, then even-keel, then leaning to the right, then even-keel. Then add in a bit of vertigo caused by not being used to being weightless in the water. Mix in some natural nerves and anxiety. Sort of sounds like being on an amusement park ride, no?
Then, top it all off by putting on a tight wetsuit, donning restrictive gear, stuffing a regulator in your mouth, and breathing in a completely different fashion than you've done for your entire life.
Eat some bland food before your next class/dive. Nothing spicy/greasy. Don't eat too much. Don't dive on an empty stomach.
Most of all... relax! You'll be fine.
Welcome to the underwater world!
Ray