Sitting down in car and felt a sudden sharp prickling pain in my left middle back and right lower chest area.last for a few seconds and happen twice.

Muscular pain: Given the duration of symptoms, your age, and the condition, I would think of it being a muscular type of pain that is probably due to spasm of the muscles from the position you are at inside the car.

Postural ... strain: 22 y/o Female says Sitting down in car and felt a sudden sharp prickling pain in my left middle back and right lower chest. last for a few seconds and happened twice. Not clear if one was in the process of getting into the car or was already seated before the symptoms. Either way most likely Positional/ postural muscle strain. Gentle rub/ massage when out of the car can help. If concerned see MD