At your age, pain in between the left shoulder and left elbow maybe due to frozen shoulder. It can also be due heart issues. There can be other causes also but those can be talked about only after examining you personally.
If you indeed have Frozen shoulder, try the following:
*Hot water bag (10 minutes twice a day)
*After applying hot water bag, apply Nobel Gel
*Tab Flexon (1 tablet after lunch and 1 tablet after dinner for 7 days) (if you are not allergic to it)
*Tab Pantakind (40mg) (1 tablet before breakfast in the morning for 7 days)
*Stand in front of a wall, keep both your palms on the wall in front of you, then slowly raise your palms up along the wall as high as you can, then bring the palms back to their initial position slowly, repeat this exercise 40 times a day
*Avoid using pillow while sleeping
*Get an ECG done (to rule out heart problems)
Next Steps
Do let me know after one week to see as to how much your pain has reduced.