Hello, My Son Is 20 Months Old And Just Recently

Hello, my son is 20 months old and just recently started having diarrhea (only 2-3 times in last 2 days) plus vomiting (2 times this morning and 2 times yesterday), but no fever. He isn't drinking much water today, but he drank 2 full cups yesterday. He is complaining/showing me that his stomach hurts him. I'm not sure if i should take him in to the ER or not.