Middle Back Pain and Mild Swelling.

I am experiencing pain below both side sholder blade (middle back area) last 5 days. Pain was mild first 2 days and noticed it increased as I did some physical work. Felt mild swelling in that area and first thought came to mild is spasm or sprain or muscle tightness so took a FLEXON MR  tablet morning and night but it didnt have much impact. So used heat plaster stickers felt better. But the pain returned on 4th day so took Movexx Plus morning one and night one... pain is gone but still feel that discomfort while sitting or holding baby in or when I work or when I sit for long period. Background I am an accountant i dont do much active recently... but was very active during my college days... so started jogging and walking after many years and do keep myself engaged stated doing some wood work at home. Felt little never problems in hand but that's common if you work physical. Those are regular... Is there any underlying reason why a pain can come suddenly in that area or swelling?