Gas formation in stomach all the time.

My mother is experiencing gas formation almost all the time, irrespective of what she eats. She is on BP, thyroid, arthritis and sugar medication for more than 25 years now. Have consulted many doctors and conducted numerous tests but results are always good, nothing to be worried about. Still all the doctors says, they are not very sure of the exact reasons of gas formation. The stomach area becomes very hard during gas formation. My mother has tried all sorts of home remedies too but no results. She experiences breathing issues also during this time and is not able to sleep. Because when she lies down on the bed she find it hard to breathe due to the gas. For many nights she just walks around in the house to pass the gas. The stool is also not getting passed properly. Regarding the food habits she is not having any spicy food or junk food. What could be the possible reasons for the gas formation and any solution to this?