Liver
It could be anxiety
It could have something to do with your pancreas.
I think I am having round ligament pain on my left side and I am not pregnant. Is this possible? My doctor noticed a cyst on my ovary on the left side.
a kidney stone.
If somebody punches you there.
Some causes would be, sleeping on left side, sprain, or a strain.
One thing that can cause left side of neck pain above a collar bone could be a stiff neck. If the pain does not go away, one should see a doctor.
acidity
heart disease or heart attack
appendix or kidney infection.
There are many possible causes of severe pain in the lower left side including trapped wind, appendicitis, constipation or muscle damage. If the pain persists, it is best to consult a doctor who can offer a full diagnosis.