Ovarian Cyst while on the Pill???

I'm 41 and for the first time, my doctor said she felt a cyst on one ovary, didn't seem too concerned, but had me set up a pelvic ultrasound.  I didn't think much of it either until I started reading up on it.  I'm reading that being on the Pill should prevent cysts and that if you're on the Pill and get a cyst, it should be surgically checked.  I wasn't worried but now I am!  And I'm thinking that if the ultrasound looks fine and the doctor says to wait a few months for a recheck I'll be worrying the whole time that something malignant is growing.  Any new info would be greatly appreciated.  My ultrasound is in five days.  Thanks very much!