Learn English – Is this correct sentence “Where have you been yesterday”

All of them sound natural to me except #6. I would say instead:

Why is my stomach burning?

or

What is making my stomach burn?

One other note, though; even though Nos. 1-4 are worded okay, I would not call those "stomach problems." The phrase stomach problems is usually used to describe ailments like indigestion, as you did in Nos. 5 - 8. A growling tummy isn't really a stomach "problem," not in the way I usually hear stomach problems.

Is there any other word which is commonly used to describe stomach related problems?

There probably are, although I think you nailed the two most common ones with Nos. 7 & 8. Upset is often used when referring to the stomach organ, while bloated is sometimes used when referring to the lower abdomen in general, and may not be related to digestive problems at all. Sometimes you might hear the term GI used, particularly in the medical community (GI being short for gastrointenstinal). You can simply Google GI problems for a boatload of examples.

This is how you read it by breaking the sentence into parts and extracting the complex meaning from it: You have been working hard and providing measurably positive results for your company,

yet

your pay isn't what it should be

or

you keep getting skipped over for a [promotion or new opportunities] to grow.

Means: you are working hard and fetching results as well

but, your pay is much less than what you should get

because you are not considered for a promotion or new opportunity to grow.