Baby doesnt want to eat

Its been over 24 hrs. He usually sucks on each side for at least 30 mins suddenly yesterday he only sucks 2-5 minutes each time and cries at the breast.

We changed his diaper once at 5 pm yesterday and is was just a little wet at 12am so we changed and thats it. 1035am still dry. Refuses to eat. He wants to cuz he's opening his mouth to suck but when I give him my breast he cries.

I didnt eat anything different. Only thing is he got vaccines two days ago.

We called his doc but they take forever.

What could be going on with him???

7 months