Why do i get stomach cramps when i eat bananas. i wasn't allergic to them before.

You are now: Anyone can become allergic to something in his life even though the same food had been tolerated before. The banana may be the same but your body has changed as showed by epigenetics.

Could be allergic: It is possible to become allergic to a food as an adult. Allergy testing helps to determine if it is an allergy or intolerance. Any food that causes untoward symptoms should be avoided at least until allergy can be ruled out by appropriate testing.