Welcome to HCM
First you have not written why you are prescribed Codeine and naproxen
they are analgesics central and NSAID group. Diarrhoea
which you suffered may be some infection?self limiting this is not necessary that every one should have diarrhoea who cosume same food.
On the cotrary Codeine causes constipation
,you should continue to take light meal also fluid and electrolytes.
Take safe potable water and follow the advise of doctor you will be alright in few days.
is acid suppresant and Codeine analgesic If required take with the advise of your Doctor
Good Luck to You