29 yr old female sharp lower back pain on the left side comes suddenly and then goes away specially when i stoop down to pick up something?

Sciatica: It's possible that you have a disc in your spine that's pinching a nerve, also known as sciatica. It;s also possible that this could be a muscle strain. An examination from a sports medicine doctor, physical medicine and rehab doctor or orthopedist can figure it out and start you out with physical therapy if anti-inflammatory medication, rest and massage have not been helpful. An MRI may be needed.