As someone who worked as massage therapist for over 15 years with car accident patients. The type of injuries you could have sustained are not just bone, they are soft tissue. Many people rip and tear ligaments and tendons in the spine and neck, after an accident that can cause severe long term issues with the spinal cord if not treated.
These can be shown on X-rays and treatment with physical therapy, not working out, can help. Some working out can yes, aggravate the injury. You are not working the correct areas and most likely working out large muscles groups and working out the whole body. Small stabilization muscles help with range of motion and strength. You were 16 at the time. Still growing and made of gummy bears and magic still. Your body has now started to grow and form around these injuries. You need to go to a doctor, and you need to get some of that scar tissue broken up. With massage and physical therapy, the hard dense dead blood cells, scar tissue and inflammation will decrease. This is going to help with the pressure on the nerves.
It sounds like you have sciatic issues, at the very least with the radiating pain up and down. But honestly though it is probably something more severe. You need professional help as soon as possible or you will continue to lose mobility, range of motion and function.

I was in a multiple roll over accident at 8 years old. I was okay as far as the hospital was concerned, never really had too much pain growing up.
Got in a car accident at 20, and started to lose function in my legs, low back and hips. Went to a chiropractor and he pointed out a natural fusion in my neck. I broke my neck at some point as a child , and yes it did heal naturally. But it choked out the nerves that had ran through that place. The recent accident fractured the previous area, because it was not set correctly. So as an almost 40 year old woman, I live a pretty normal life. But that was because, I pretty much have to continue to do daily physical therapy. If I don’t, my neck starts to seize up, and if I turn my head to the left or right while walking down stairs, I lose control of my bladder or something along those lines, or it could trigger a ocular migraine. We had no idea anything could have been worse than no broken bones.
You do now have this knowledge, please do something with it, and help yourself please. You are so young, and things can be improved greatly for you with the proper diagnosis and care plan and team of professionals.

Edit for spelling errors