Thanks for writing your query.
Pain and weakness in left arm can be due to various reasons common being overuse of the arm, resulting in muscle spasm, fibromyalgia
,etc. Pain in left arm due to cardiac origin is possible but it is usually associated with some other signs and symptoms.
Taking pain killer like Ibuprofen
twice a day after meals along with antacid like Ranitidine
150 mg will be helpful in relieving your pain. Do hot fomentation and apply some pain relieving gel. Also give rest to your left arm.
You should get an ECG done and consult a Cardiologist
I hope this is helpful to you.