No ideas what it could be, I'm sorry. You should see your doctor about this. You could have strained something or you could still be hurting inwardly from your car accident. The best thing to do is not assume and get an appointment so that way you have covered all your bases.
Best of luck.
It could be a condition called costochondritis and you can try any NSAID.. and see if you feel better in a week. If it persist after that do see a doc.
Welcome to the MedHelp forum!
Chest pain aggravated by laughing yawning, moving in certain directions, stretching and deep breathing goes more in favor of costochondritis, which causes pain and tenderness at points where your ribs attach to your breastbone. The inflammation around the joint area gives sharp pain on taking a breath. This can also cause tenderness on pressing the area which pains. An orthopedic doctor can diagnose this for you. Generally there is no cause. However it can be due to infection, blow, injury, or fibromyalgia. It usually goes away on its own. Otherwise it can be treated with muscle relaxants, and non steroidal anti inflammatory drugs. It can also be muscle pull. Shingles can also start this way. Take care!