Why am I still so sore 2 weeks after a car accident?

You were in a mva. The human body does not like car accidents. The muscles are sore, the skin is bruised. You should start feeling better day by day week by week. If not make an appt with your doctor.
That's expected. Motor vehicle crashes are associated with a larger transfer of energy into the entire body. The soft tissue injury can take up to 6 weeks to resolve. You need to see your doctor to get proper pain management.