Do you notice if his legs actually give way or is it that he just loses balance?
I would perhaps ask for another check (eyes and ears) and also for a check of his hips/legs. This isn't advice - just saying what I would do if were me. The fact that your DS had been walking fine for 2 whole months, does imply that something isn't quite right.
I know older children can fall/trip over a lot when their feet are having a growth spurt but not sure if it would happen so obviously in a little one like your DS.
Is he doing something else important at the moment, like learning lots of new words or learning to put words together or something? I found my DD went through a wobbly and clumsy phase when learning something that took up a lot of attention sometimes.
His shoes are fine as they're new so all ok there. I have notice he's worse when wearing his slippers which look to curl his toes over so I took them off him but he still does it without them or with his shoes on.
He is learning new sounds and trying to copy when we speak yes and he's also teething.
I think I might get him checked over again though thanks.