Okay, Oscars are egg layers, they don't give birth to live young. However, their abdomens do become slightly swollen when they are egg laden. I would like to see a photo of your Oscar if possible. How long has the abdomen been swollen? a female Oscar well indeed lay eggs without a male present, obviously you need a male to fertilise the eggs so if eggs are laid, they won't hatch.
Oscars are notorious for moving things around in their tank, this can be rocks, ornaments, plants and substrate. Whereas this kind of behaviour is often part of breeding practices, it doesn't indicate that they are going to start breeding.
Many Oscar owners will tell you that their Oscars do this on a regular basis. That's why if you keep Oscars, for get having a nice pretty tank, they often make it look like a bomb site.
Hope that helps, like I said, I would like to see a photograph of your Oscar, whereas I don't want to worry unduly, swollen abdomen is something that you have to address if the condition carries on for a while.