Hi behemouth - S**T probably isnt a word you should use as we get all ages here, but i have to admit your bluntness made me laugh.
Sexing convicts
Male - larger, more aggressive, extended dorsal and anal fin, nuchal hump, poss. brighter coloured
Female - the opposite plus an orange belly + / - orange around the darsal area.
It might be that you have a breeding pair and that big belly is eggs.
It might be constipation - in which case shelled peas or epsom salts are the way to go.
He might have gorged himself on food?
Is he / she behaving okay?