You haven't mentioned your age. Left sided chest pain
can have many causes, the most common being an issue with the heart. If you are middle aged, go for a stress test
to rule out cardiac problem. If you get the pain on inhaling, then it can also be purely muscular. Pleurisy
is less common since you are saying you have had this problem since quite long.
Absence seizures usually do not cause a left sided chest pain. They cause a generalised tiredness
and ache in the body post-seizure.
If there is tenderness in the left side along with the pain, then it can be inflammation of the costal cartilages.
Do not take painkillers blindly. Get your pain checked. It can be something absolutely harmless but it is always better to be cautious.
All the best!