Hi, I had that disease from my daughter's EX-daycare this summer. Mine was really bad where I had flu symptoms, severe rash all over my hands and feet. My hands were in so mcuh pain that I couldn't pick up stuff and dress my daughter with anything with buttons, and my feet hurt so bad that I couldn't walk. It was just horrible. Thank god my daughter didn't get it, but my doctor said it's a very common disease among kids in daycare and preschool, but she said mine was one of the worst that she's seen before. But there was nothing that she could give me to make me feel better. She said I just have to wait for it to go away. And it did. It took a long time and took a long time to heal and I looked like a monster and felt like someone with horrbile disease, but just glad that it was me not my daughter who was only 4 months old at that time. By daughter is no longer at that daycare where I got sick from because she came home with whooping cough, 2 pink eyes, and 2 viruses in only 4 weeks.
My doctor said it's something that is very common among young toddlers and kids as I mentioned, but hopefully, your son won't get it again.
Good luck and I hope your son's hand, foot, and mouth disease goes away soon!