I Got Into A Car Accident Yesterday. I Was Rear

I got into a car accident yesterday. I was rear ended very hard. About an hour or 2 after the wreck I broke out with a rash on the front of my neck back of neck on my shoulders & some on my arms. The hospital that I was transported to treated me awful so I left without getting checked out. I went to my chiropractor to have xrays done on my neck but he could not explain the bumps coming up. They are getting worse as the day goes on. What would cause it?