Help with 2001 Mazda tribute

I bought a 2001 Mazda tribute, first week nothing wrong. Then I couldn’t start it, it would turn over but not start. Changed batter. Fine for another week. Then same thing happened, auto part store said batter is good so is altanater. At work could not start, had to push gas peddle to floor to start. Took to a mechanic they found nothing wrong. They checked fuel filter and sensores. I changed to higher gas grade and try not to go below half a tank.
Need help.