Thank you for your query on Healthcare Magic.
Vomitings may be due to gastritis.
You can give an antiemetic like Phenergan
in prescribed dose if the vomitings are continuing and this will decrease the itching also.
Give sips of ORS to prevent dehydration
The rash in pelvic area is due to some skin allergy
Apply a calamine containing lotion externally.
You can give zentel, but give in prescribed dose after consultation with the pediatrician
Hope I have answered your query.