Son Just Out of Nowhere Started Screaming in Obvious Pain

I'm a FTM and just a few moments ago my son began screaming terribly out of nowhere. He's been a bit constipated, but he wasn't having a bowel movement. Last Saturday I took him to a walk in clinic where the l doc said he had a middle canal ear infection. I started him on the antibiotics that day, but he hasn't had any sort of reaction to the medication. I have no idea where his pain came from, but it just scared me to death! I've never him scream like this, he was arching his back, he was red in the face. I gave him some children's tylonel and he eventually calmed down. Now he's back to his old self, but it was so out of character. The whole escapade was about 7 or 8 minutes. What could it have been? Do I need to follow up with his pcp? Did I do the right thing? My heart is still beating. So scary not knowing what's wrong or how to comfort.