Ovarian cysts from Mirena?

I just got my Mirena 4 weeks ago and went today for the placement sonogram. The Mirena is placed great but when the doctor check around to my ovaries he found what he believes is a cyst. It wasn’t there when I got my Mirena so it’s developed in between. I’m guessing it’s the the size of a nickel? I’ve never had a ovarian cysts before so I’m wondering if anyone has experienced this before. I had read online that Mirena can cause cysts but they usually disappear. I had an IUD a year ago before I got pregnant that was there for close to 5 years with no issues.

I go back in 6 weeks for a follow up sonogram to see if it’s gone. He said if it’s not then they will treat it. Doctor told me not to worry because most of them go away as long as it’s not a growth. Which I don’t like the word “growth” lol.