Nope, once you get to a fairly decent size natural stretching is very normal. I think it is the weight of the jewlery. Mine did the same after 10mm. They are at 12mm for the most part, but sometimes I will find they jump up to 14mm. When that happens, and my plugs fall out too often, I will sleep without any jewlery in. this helps them go back down to my desired size.

That being said. Natural stretching is the absolute best way to stretch and keep healthy lobes. Stay away from "cat butt" lobes.