Hi Renee, Yes I have had large single and benign cysts on my ovaries in the past. Not through a pregnancy though. They can usually tell what sort of cyst it is from the structure of it by the ultrasound. In the past I have usually just had a follow up ultrasound several months later to make sure it has gone away by itself.
Best thing to do is to speak with your GP or OB straightaway as that will give you the best information without you having to speculate!
((hugs)) cos i can tell you are worried about this!