Starting the car problem

I have a problem to start the engine sometimes especially if I drive the car without stop for 30minutes and once I stop the engine and want to start need to start the engine at least more then 5 times then the engine can only start. It seem like the car no petrol or fuel pump problem but I have change the fuel pump still having the same problem. Once I start the engine the RPM no stable and I press the petrol pedal and engine died and sometimes feel like start the engine the starter running only and engine not running. It need to start many times then only can start the engine. What the problem? Please advise. Thankyou