Here you have given symptoms of left
chest tightness, pain in left shoulder blade along with lower armpit and
biceps.
As per your symptoms there are couple of possibilities.
If you have chest congestion and
chest discomfort then it can be related to lungs and I suggest to take x ray and check properly for any sort of lung issue or
chest infection.
If there is no chest congestion and its only tightness of left side chest then it can also be related to cardiac issue. I suggest to visit cardiologist do your ECG along with treadmill test to evaluate further.
If there is no issue at lung and heart level then it is
muscular pain only at left shoulder blade which is radiating to left side chest as well as armpit level. But this pain can also be indication of problem at
cervical spine like loss of cervical curve or disc related issues. How ever for this I suggest to visit orthopedic doctor and get yourself evaluated properly and take treatment as per that.
Here I suggest do visit a physio for further treatment planning as per orthopedic suggestion because
physiotherapy treatment will help you to overcome the pain as well physiotherapy exercises will help you to improve the biomechanics of cervical spine, shoulder blade as well shoulder joint which will further help you to have long term relief.
You can Also use hot pack at home for some more pain relief. And do apply some pain reliving ointment after the use of hot pack.
I am sure this will be helpful for you if you use it properly and follow the suggestion. Take care.