1999 Pontiac Grand Am It doesn't want to start and stalls

1999 Pontiac Grand Am 4 cyl Automatic

A couple of day ago when I try to start the car I dint want to. I was in a flat parking lot, I turn off the a/c just in case when I try for the second time but still it was like I want to turn on but not. At the 3rd time it did it. Again the same day it did it this time turn at the second try. It was taken to the shop to do a oil change because it was do I told my husband maybe is that because I check and it was really dirty. The mechanic said it has a little lick but is not a big deal. The next day it did it again and my husband decide to tell me, it did it before to him. Now yesterday he said when driving he have to stay at a speed constantly because it start wanting to turn off if he slow down. I'm the one that takes care of the car and I have a couple of theories but I want a professional opinion before I spent money on it. Alternator, sparks or fuel filter, fuel injector. What should I check first or should I take it to be check with the machine to see what it says. Thank you