Cyst or endometriosis

So Ive always been regular with my periods but I had one month where it lasted 2 weeks so I went and had an internal scan and an ultrasound and they said it COULD be endemetriosis Or it COULD be a cyst. Ive had no symptoms and my periods have gone back to normal. Do I need to worry? Will this affect my chances of having a baby? Im really worried as I have to wait until September for repeat scans, but I do have no symptoms. Ive been pregnant 3 times previously by the way.