gas smell

I have a 1999 Buick Century and recently I've been smelling gas fumes when the widows are down or if the heater is on. I changed the fuel filter but that did not help. If anyone has any ideas on what it might be I would appreciate any input.

Have your dealer run your vin for recalls on fuel pressure reg.
And raise the hood and have a look around.
Also look on the underside for gas leaks and take a look where you changed the fuel filter.
Where there is a smell there will be a gas leak.
Mt