Regardless of the cause... your description sounds like excessive fuel is getting into the exhaust, if not leaking ... this could be dangerous (as in fire) as well as kill your cat from the rear bank of cylinders (#6 is the one nearest the driver on the firewall side of the engine). if not the third one also.... since you believe gas is coming out of the tail pipe. You might pull the cap and plug from#6 to evaluate for gross abnormalities, gap, oil fouling, etc. the "white smoke" could just be water vapor as we commonly see. BUT I would echo SHOdded and nmb...
Let the dealer evaluate this is IMHO the best and safest thing to do.... and I personally would have it towed to the dealer rather than drive (maybe you still have some warranty and roadside assistance0