Wish there were a really good way to prevent these cysts, but so far nothing has been determined. Sometimes Birth control pills will help since they suppress ovulation. No ovulation, no cyst. Cysts are really a normal part of the cycle.. it's just that they sometimes don't "disappear" as they should. You may want to check out the "Health Pages" at the top right of this page. It has a lot of information about cysts.
I'd ask for another TVUS to check things out in any case. Don't forget though that cysts are very very common with younger women., and very rarely anything to worry about. You may also google "Ovarian Cysts Birth control pills" and it will explain why they are sometimes prescribed to suppress ovulation. It isn't 100%, but seems to have helped a number of ladies here.
Good luck and let us know,
Sandy
It is only rarely anything to worry about. Most cysts are benign, especially are your young age. There is no real way to prevent cysts, except to make sure you have regular periods. Going on the pill can help with that. Talk to your doctor and have him/her do another ultrasound. He/she needs to know how big the cyst is this time, if it is still there. It might have grown, you might have multiple ones, or it might just not have disappeared and be the same size. You still need to know though. If it has grown, then your doctor can decide to either monitor it for a few weeks and put you on the pill, or surgically remove it, depending on the size and its components; whether it is still simple, or complex. Either way, most cysts are benign and I'm sure you have nothing to worry about.