My 3yr Old Boy Had A Fever Of 102.6 Into

My 3yr old boy had a fever of 102.6 into night (two nights ago) after couple doses Tylenol. Fever finally came down next day with Advil but didn't go completely away. the following day he started with diarrhea which continued all day then started vomiting last night x1. Seemed feverless for am today but then midday He had a fever of 101 that came down after Tylenol but has continued with diarrhea and now vommitting has increased with c/o stomach pain with it. Hasn't had a fever for several hours but vomitting, diarrhea ,stomach pain with the vomiting (his belly feels a little hard to me) and loss of appetite all weekend. I am worried. We are going to see md tomorrow, but he has never been this sick before. We have been working to keep him hydrated. But as the vomiting gets worse I am afraid it won't be effective. Any thoughts?