Forget about chemicals, they flat don't work. Your main drain is likely partly clogged and it is more than a hand DIY snake can reach or clear if it does reach it. Often they will just poke a hole through. You need to call a professional plumber who can use professional equipment to auger clear to the street or septic tank. Anything else is just a waste of time and effort. It is possible that something has fallen into the toilet that is wedged in the trap. Common things are kids action toys, makeup kits, shampoo bottles, etc.. The toilet auger probably just goes around them if that's the problem. If you think that is a possibility, you could pull the toilet and see if you can locate the jam from the underside. That's fairly quick and easy, and it's lots cheaper than a plumber.