If you really mean 'slang', you could say
'...I've got the squits and me belly's proper knackered.'
'...I bin screwed over by them old farts at the tax office an' I'm fair skint.'
If you mean 'informal or colloquial terms', consider
'...I've got to take my dad to the dentist'.
'...I'm not feeling at all well'.
'...something' unexpected's come up that I have to deal with'.