Hopefully we can rule out the extreme, a very rare stomach tumor. Going to another more happy and realistic direction for the cause, any change in diet? Some whole grain products are not suited for everyone. Soy and other types of beans can cause (like whole grains) a blotted feeling, most of the time. Quite a few protein powders, though claimed to be of high quality, use a lower grade of soy powder as fillers. Just because it says "Super Duper Whey Protein" on the labe does not mean that it's a 100% pure Whey protein, or even 50% for that matter. These often upset the digesting abilities. Even vitamim and other so called, high priced, BB'ing supplements are just really cheap grade that can be guilty of this stomach discomfort. Always good to read a label for extra caution, before using. Even my beloved paste, pizza and Mexian foods (my main food groups) have been found the villian for some folks. To me, it just sounds that you have a gas build up from poor diet selection. Working the abs should never cause any problem like that for most people.
Might want to try a little test and drop all extra BB'ing (even whey protein) supplements (if you use BB'ing supplements, that is) for a week or so and see if the discomfort goes away. Along with this, see if you can avoid grains/soy and other like product at this time. Go more towards meat, chicken or fish as the main core of the diet. All three are major muscle building foods anyway. If results are good by this plan, than try adding a supplement a week, along with select grain products, and watch for any negative results.
If still a problem, than food alergys could be the blame. Good luck.
