What is wrong or needs to be fixed in my car?

If you're using oil but there's no leaks, it must be burning it. It means your piston rings are are leaking by. If you follow while someone else is driving, watch when they step on the gas, you'll see smoke then. You can either get new rings (best) or use a higher weight oil like 5 W 50. It is thicker and will not blow as much oil but it's not a real fix. You need an overhaul.