my baby just turned one! 😭😆

So yesterday we celebrated my little guys birthday and it was pretty hot and our home has no AC so we spent it out doors keepin him as hydrated as possible. Well during our time out he caught a fever and it's still here 😔 his father noticed that he is crying when going poo.... We transitioned to milk a week ago with no issues till yesterday. Has anyone else experienced this before?  And on another note , happy birthday to my baby boy!