When should I seek a pain expert?

This may depend on the type of pain, ie. sharp chest pain calls for immediate help vs. muscle soreness or aches which may subside. A general guideline I use is as follows:

Soreness, a dull ache in muscle a day or two after exercise/activity. It fades in 2-4 days.

Strain, sharp and sudden pain focused on a particular point caused by a specific movement, ie. fall, lifting heavy object, stretching too far. Typically lasts 1-3 weeks but if pain returns when resuming activity, consult primary care doctor who can decide if you need a specialist.

Sprain, a joint twists unnaturally, popping sensation & intense pain caused by an awkward move. Common in wrists, ankles, & knees. Lasts 2-3 weeks or 4+ weeks if severe. If swollen & won't support weight after 24-48 hrs, may need MRI to determine if torn ligament or broken bone.

Overuse injury, a nagging pain gradually increasing & staying, ie. tennis elbow or runner's knee. Typically from repetitive movement. 2-4 weeks rest from activity. If after rest period, pain persists or gets progressively worse, schedule with a sports doctor who can diagnos & perscribe treatment.

If you have suffered a significant event that causes injury to your body due to a mechancial trauma like being in an car accident, injured during sporting activity or you can relate a specific incident to your pain or discomfort you should consider seeking advice.  Another reason for pain can be overtraining.  Pain that lasts more than 2-3 days could indicate a strain or just pushing more than your body is ready to perform with daily activities or exercise.  Often times this will relieve itself with rest (so take a day off).  Finally, if your getting specific pain that is nocturnal (night related) and it keeps you from sleeping you might also consider getting evaluated by your physician or health care practioner.