2000 Pontiac Grand Prix Car won't start

Engine Mechanical problem
2000 Pontiac Grand Prix V6 Front Wheel Drive Automatic 146000 miles

My car has 146000 km's (not miles).

Recently my car has been intermittently "surging" and "hesitating" on the highway (ONLY on the highway) and my RPM's would jump up and down sporadically when this would happen.

Then my check engine light came on, the code indicated a faulty O2 sensor behind the catalytic convertor. I replaced the O2 sensor behind the cat. We thought that would be the reason for the surging/hesitation/rpm jumps but the problem continued (again, ONLY on the highway). It appears this was just coincidental?

Today, I loaded up the car, buckled my daughter in, and now the car won't start.%&$#@! It sort of sounds like I am out of gas. I have checked the obvious, car is in park & there is nearly a full tank of gas. I last started the car 2 days ago without any problems.

Any thoughts?