I’m confused on why my stutter came back.

I’m confused on why my stutter came back. I used to have a bad stutter when I was younger and it went away over the years, I went years without having an issue with stuttering. It would only come occasionally. I am now 18 and have found myself picking it up again. I have been having this issue again for the past 3 weeks and it’s seeming to become more of an issue every day. Does anyone know what exactly could cause this and has anyone experienced a period where their stutter came back ?