In the past 3 weeks, almost every time l tried starting my car, l have to press hard on the gas for 20 seconds or so in order for the car not to turn off. Then it goes well and drives perfectly. Is it from the spark plugs or the fuel pump?

Could be the fuel pump but l would have the fuel system cleaned first. The intake etc. Could actually be that simple.

Actually, the first person might have your answer. It sounds like a fuel system issue. Has your car been through all the major services? If you had done everything up to this point. This might be a simple issue to resolve, but a shop would be a good place to find out.