What Causes Chest Pain?
cardiac cause very unlikely.
Detailed Answer:
Hello dear,welcome to HCM forum.
This pain is very unlikely to be cardiac,because:
1)Sharp nature of pain-cardiac pain is a very vague/diffuse discomfort or heaviness rather than pain.
2)Pain on breathing-cardiac pain will not have any relation breathing.Pain on breathing indicate either pleuritic or musculo skeletal pain.
3)Two normal ECGs
4)Cardiac pain not much common at this age group(unless you had longstanding hypertension/diabetes/hyper cholesterolemia/smoking).
From your description,the pain seems more likely a pleuritic pain(due to irritation of pleura-the covering of lungs).
Rather than ECG,a chest examination and chest X ray will help.If everything is normal,this just need simple analgesics for 5-7 days.
You can follow your doctors advise;nothing to worry for sure.
Hope this will answer your query.
Wishing you good health.
Thank you.