Help! My 19mo is suddenly walking differently and tip toeing on one foot

He started doing it 3 days ago, and he does it only on his right foot. He’s been walking normally for 6 months. It just started out of nowhere and I’m with him 24/7, so I don’t recall any injuries or anything, and he doesn’t seem to be in pain or have any bruises or marks. He’s still both walking and running, but he’s doing it so often, with and without shoes. It’s causing him to walk funny and it’s really worrying me. Google is scaring me. When I went to get him out of his crib this morning, I was hoping it had cleared up but as soon as I put him down he started doing it again, up on his toes on his right foot. It’s also intermittent, it doesn’t happen with every step, but very often, probably 70% of the time. We have his 18 month well visit this week so I plan to ask then, but just curious if anyone has experience with this in the meantime? Thank you.