Why won't my 1991 honda civic hatchback won't turn over and stay on

You either have a weak battery or bad starter. First clean your battery terminals and make sure everything is tight. Try jump starting it. If it turns over and runs, put a volt meter on the alternator. See if it is putting out at least 14 volts. If you don't have access to a volt meter, go to Autozone. They will test it for you. If it seems okay, it's most likely and old weak battery. If jump starting it does nothing, all you hear is a click, I would suspect a bad starter.

My starter is good and battery is new and it just won't turn over and now there is gas in my oil ?

Sounds like you have a serious problem. If fuel injected, it seems that you have leaky or bad injectors. Dumping too much fuel into the system. That's why it will not fire. You may have an injector stuck open, or a bad fuel regulator. Change your oil. Get it to a shop immediately if you are not going to fix it yourself.....