I find I am having trouble digesting oats, rice & wheat. (bloating and abdominal discomfort)

I can tolerate them if I have a small amount, maybe 1/4 cup cooked oats / rice or 1 slice of bread.

I am not sure if other grains bother me yet.

Has anyone had this problem? Is there something to help with this? I tried Beano.

What do I put into my shake?

Thank you for your help.
Vicky