A catalytic converter is designed to increase the temperature of the exhaust to convert hydrogen sulfide to sulfur dioxide.
The reason you are smelling sulfur in your exhaust is one of two things.
The titanium within the cat has been used up or burned off over time. Since the dense titanium is not retaining heat any longer the steel or other material it is bonded too is getting coated with carbon and insulating the internals of the cat and thus preventing it from getting to the temperature it needs to be at to complete the conversion process from hydrogen sulfide to sulfur dioxide. Thus the scent of sulfur.
The cat is actually clogged and preventing the exhaust from escaping in the normal freer flowing manner. The restriction in the exhaust causes too much back pressure and is effecting the combustion process in the engine and giving you performance related symptoms.
You may receive engine codes and have a check engine light on.
You can go to a local car parts store and many of them will connect an ODBII tester to your vehicle to get the error codes that can tell you what components you need to replace.
Cat converters can be expensive due to the titanium used within them to retain heat in order to convert the hydrogen sulfide to sulfur dioxide.
Best of luck