So i have 4 oscars (3 of them about 4-5 inches, one being about 3-4) and a jack dempsey. All of my fish are doing perfectly fine except for one of the larger Oscars. I just noticed it this morning, but it sits on the bottom for a while and then every once in a while it will swim around again and then sit. It still ate normal, and looks normal.

Will this clear up on its own or what? I will do another water change today.

Have you tested your water? That's what we need to know before we can help. what are the Ammonia , Nitrite, Nitrate, and PH readings?

It may be your o is just sulking and being moody, but we need those waterparameters to make sure there are no other problems.
How big is your tank?