It may be a problem with your alternator unfortunately.

Your alternator is what converts the mechanical energy from you engine, into the electrical energy that is used to power all your cars accessories. It's also what keeps your battery fully charged and gives it the power that is required to start your car. When you alternator isn't working properly your battery starts to do the work for the alternator which is not what it's designed for. It's meant to be more like a capacitor than a long-term power supply, and basically just give a huge boost of energy to start the car. If the alternator is failing and the battery is working overtime, eventually the battery will go flat. Because it's not a problem with the battery, the car is still able to be jump-started, but as the alternator is still not charging the battery, the car will probably not start again by itself, and may even just stop while driving.

Fingers crossed it's something much simpler than that, but it just sounds suspicious to me.

PS. Can you tell my daddy is a car mechanic? Hehe