As you had cardiac check up done are with in normal limits , it is more likely due to noncardiac causes .
Common non cardiac causes for chest pain on left side are
1 muscular pain
related to muscle or joints
2 cervical spondylosis
- disease of vetebra which is also common in middle age
3 any blunt trauma
to chest wall in recent past
4 some times pan due to acid peptic disease
may also cause chest pain on left side .
5 ver rarely infections like herpes zoster
can also present with pain like you have , but they will also have skin lesions and pain will be intense .
Consider low dose of analgesics and antiinflamtory drugs for one week in your case .
Lastly you need not be anxious about this as it is not related to heart .