Having stomach issues caused by fizzy cola and ice (7)
I believe the answer is:
coeliac
'having stomach issues' is the definition.
(coeliac can mean relating to the abdomen)
'fizzy cola and ice' is the wordplay.
'fizzy' indicates anagramming the letters (I've seen this in other clues).
'and' means one lot of letters go next to another.
'cola'+'ice'='colaice'
'colaice' anagrammed gives 'COELIAC'.
'caused by' acts as a link.
(Other definitions for coeliac that I've seen before include "of the belly" , "Relating to the abdomen - ice cola (anag)" .)