Thanks for your query. We would have appreciated if you had mentioned the antibiotic which your son is having for his ear infection
. At times the antibiotic can cause increased frequency of motion which is not watery as in your son's case. We would suggest that you discuss with doctor who has prescribed the antibiotic who shall guide you further. Water melon seems an unlikely cause for such a prolonged frequency of motion.
Wishing your son all the best.