It sounds to me like something in your exhaust system isn't lined up proper.
I have found that if you have to "force" two exhaust pieces together and relying solely on a gasket to keep the seal ...... it will usually, eventually leak.
I suggest you get your car up on a rack, remove stuff so you can get at the exhaust system, disconnect all exhaust pieces, find out where they aren't mating proper, bend them to fit together better then put the whole system back together with new gaskets.
Easy for me to say ....... right ....
humfrz