How can one anticipate when someone will be feeling bad at a particular point? Or is this like the colloquial meaning in English (He must be feeling bad because he's done something wrong)?
In either case a little context would be helpful: "Your son will be feeling bad because he broke your favourite cup." Or "Your son will be feeling bad tomorrow after eating that soup."
Besides, a more natural wording in English might be "Your son won't be feeling well", but again it depends on context.