1997 Cadillac Deville My car wont start the first try

Hello everyone im havin a problem with my car that has been going on for the past 4 months or so. Everyday when I go and start my car, I put the key in the ignition and turn it but instead of starting my engine makes this noise like its trying to start but cant. After the second or third try it finally starts, the weird thing is that once the car starts, I can turn it off and on and it doesnt make that problem, it only does it after the car has been parked for a few hours.I took it to a meineke mechanic and he said its not the starter, he said its most likely the fuel filter, but I have recently replaced my fuel filter about 4 months ago. He also said it might be the fuel pump. Since the fuel pump is very expensive I would like to replace or clean any other components that might be the reason for my engines misfiring.I have replaced all 8 spark plugs, and wires, I have also recently cleaned the fuel injectors (the $3 bottle you put in the tank), my mechanic also replaced a faulty o2 oxygen sensor that was badly burned just yesterday. With that said what can be the problem to this annoying and humiliating problem?