Very hard to tell without testing as there are many different potential causes.
Kids, unlike adults, tend not to dwell on what pains them, especially if they can be distracted by more pleasant stimuli, or if they are cheerful/active by nature. This is actually what makes it so difficult to assess children's pain: kids tend to ignore pain until it becomes unbearable.
Regardless of what your child has, vomiting over an extended period of time is ALWAYS very damaging. Pls see your doctor.