Hello!
Collar bone is referred as clavicle and simple non displaced clavicle fractures heal without any assistance. The reason for surgeons not attempting repair for minor fractures is because of the large amount of important structures located in the neck. Collar bone will heal with a sling and restricted movements.
After the car accident ample rest and restricted movements would have healed your collar bone. After 3 years the pain may not be related to the previous accident as you did not have any pain in between. It is worthwhile to go for an X-ray initially to rule out any problem with the clavicle.
I suggest you to take a complete review about your back/spine, expert orthopedic examination and MRI reports are required here and you also have to find out any spine problems which may be related to referred pain elsewhere.
Also I would suggest you to review your shoulder for arthritis, any injury to any ligaments and also recollect if you had any injuries, falls and your detailed history of your military training/injuries of the past years will be very helpful.
Also ask the Orthopedician for reviewing thoracic outlet syndrome.
You can take some intermittent anti inflammatory drugs and after diagnosis go for a proper course of treatment.
Take care!