Hi,
I found someone online with the same sort of problem with one of their pigs, they took him to the vet and were told it was a possible Vitimin C deficiency.
It could also be Vitimin D deficiency. One of my piggys recently started walking funnily, (hopping like a bunny with her back legs, instead of walking or running normally with all four legs), and we found something that said Vitimin D deficiency. I started moving them outside during the day (they live in my bedroom overnight), and she is now walking perfectly normally. A couple of them had passed away after not walking normally and not being able to hold themselves up. They also were having dental problems, snapping teeth, completely losing them. Once they were put outside every day and getting sunlight, that all slowed down.
If your piggies are inside constantly they may have a deficiency so they need to get outside with direct sunlight, (A good way to do this is in the early morning and late afternoon).
If it's not that it could be an ear infection, which can cause a head tilt, wobbly walking, walking in circles and rolling on the ground.
He could also be going blind which can cause a head tilt and wobbly walking