This is normal.
Half the body grows then the other half grows and back and forth. This is where deviated septums come from and teeth that aren't centered under the nose and a bigger ear on one side or an eye that is a tiny bit different on one side.
This is perfectly normal. For a 3 year old you might want to consider giving them half a dose of Motrin right at bedtime so they'll sleep through any light pain. Not every night of course but if they seem to be hurting at bedtime or if they had pain the night before. For a couple of days until that growth spurt is done and the other side starts. AND each side might be completely different. One side might hurt and make them scream but the other side is...wired differently and never give them a bit of pain.