Rash on my 13 month old.

Not looking for medical advice at all and I will be consulting his pediatrician if it doesn’t resolve itself by the morning. But how long after the onset of a rash should you be concerned? 2 days ago my son showed signs of a rash on his body. We hadn’t changed anything in his care regimen at all and he hadn’t tried any new foods. He is 13 months. The only thing I can think of is that he got his 1 year vaccinations on the 13th and it did include the measles,mumps and rubella vaccine. On the pamphlet it did say that they can experience a rash up to 2 weeks after the vaccine that can mimic any of the above illnesses so that’s what I’m thinking it might be. BUT, It did also say that if they have more than 50 bumps to seek medical advice so I will be contacting his doctor. The other thing could be that we were at the childrens hospital about 2 days prior to the onset of the rash so it’s possible be picked something up from there. Here is the rash. It has gotten significantly worse over the last 24 hours.