Ovarian Cyst?

Gemma
(Apologies if not in the correct group, but I wasn't sure where this topic fit in exactly) 
So I went to my OB/GYN today to check up on my iud that I got a few months ago. They told me the iud looks perfect, but they found a cyst on my left ovary. I'm 19, so this is really the first "bad news" I've gotten from any doctor. It's 5 cm, or about the size of a golf ball. (Is it just me, or does that sound massive to y'all?) They played it like it was no big deal, and told me it happens to a lot of people and that it will probably go away by itself, but I have an appointment in a month to check up on it just to be sure. I'm really curious as to see what others' experiences with ovarian cysts are. Does it happen to a lot of people? Help me calm my anxiety.