Hello,
Thank you for asking at HCM.
There are several things that can cause stomach pain and
skin rash.
The two most common are 1. a viral infection that is causing the gastrointenstinal symptoms and the skin rash also. This is generally self limiting and takes few days and gets better. Meanwhile the child should take painkillers and liquids and if no improvement or any worsening has to see the doctor. make sure you keep him well hydrated. If his general appearance and energy level is not good you have to send him to the doctor soon.
2. Allergic reaction- can cause gastrointestinal symptoms and
hives. if you know that the child has ingested something that he is allergic to this is the most likely diagnosis. in this case make sure you keep him hydrated, give pain killers and some OTC antihistamines. If no improvement or any worsening or he gets eye or
lip swelling or short of breath this is urgent need to go to the hospital.
A rare cause of gastrointestinal symptoms and skin rash is a rare disease called Henoch Schonlein purpura- this is a self limiting disorder that is generally benign but needs to be followed up medically.
I would recommend you to send your child to see the doctor and the doctor will have to decide the diagnosis and proper follow up.
Hope this is helpful and answers to your question