the ibs can be triggered by artifical sweetners, caffine, acidic fruit and too much veg and fruit fibre.
caffine can give you a lazy bowel and are best avoided.
I find personally that one cup of coffee creates an instant dash to the small room iyswim as does chewing gum or ANY food with those sort of sweetners.
working out your individual levels of fibre can be difficult, for instance a very small amount of baked beans are ok, but more than say 3 tablespoons can cause my symptoms to return.
changing from wholewheat bread to white bread worked wonders on my gut pain , bloating and wind, so the weetabix might be too much fibre in one go if he has symptoms like that.
very high fat foods on an inflamed bowel can cause symptoms to return.
so regular meals, with small amounts of fibre throughout day, with plenty of water to drink, helps.
a warm bath for tummy pain, and anything else to de stress .
there are more nerve endings in the bowel than in the brain, so any bowel pain is quite nasty, stress is a major factor in this, if you know that child is going to go through a more stressful time, make sure diet is carefully planned to help through this period.
does your child need to have constant dashes to the loo or wishes that he could? how windy and bloated is his tummy?
have you considered an elimination diet?
the lip swelling is of course oral allergy syndrome (OAS) and those foods are best avoided. How well controlled are the environmental/pollen allergies?
There is a wide rainbow of response to OAS, my son has this, lip swelling tingling mouth and throat. we avoid the triggers and treat like any normal allergy reaction within our action plan.