Thanks for your question on Health Care Magic.
I can understand your concern.
Yes, you are right.
Lung infection can cause
referred pain in shoulder region.
Lower lobe
pneumonia often cause diaphragm irritation. Diaphragm and shoulder joint share common nerve supply. So pain produced by diaphragm irritation can be felt at shoulder joint.
You are also smoker, so chances of lung Infection are higher due to poor lung defense.
So better to get done chest x ray.
If chest x ray is normal than no need to worry for lung infection.
Sometimes
musculoskeletal pain can cause similar symptoms.
So take painkiller and
muscle relaxant drugs. Avoid movements causing pain.
Apply warm water pad on affected areas.
Don't worry, you will be alright.
But first quit smoking and rule out lung infection.
Hope I have solved your query.
Wish you good health. Thanks.