first and foremost, it would be really helpful if you give a full detail of what you done to your car and what you are experiencing with your ride.
You have first mentioned that you have problem starting your car and it need a few crank before you can start the car.
Now you mentioned that your car start jerking and engine stalled.
From the description aboves, it is highly likely that your crankshaft sensor is about to fail.
I have the same problem with my E36, sometime cannot start the car. If can start, the car will stalled for no reason
after driving for about 100km. if it stalled, I can restart after half an hour or so.
Finally one day the car stalled on the highway and have to call my regular workshop. They changed the crankshaft sensor based
on my description and the car start instantly after changing the crankshaft sensor.
Hope your problem is the same as mine.