It is entirely possible thaty you could be lactose intolerant.
There is a simple breath test
that can detect this condition.
Other possibility is ingesting high amounts of sugar can
cause a"Dumping Syndrome" resulting in diarrhea
One way is to completely avoid all dairy products and
any snack that contains lactose for 7-10 days and see if
your symptoms go away. Then you know.
As for spicy foods affecting your stomach,you may have
.You can try taking either drug like Zantac or
once a day and see the response.
wish you well.