In my opinion u have strained ur back due to prolonged sitting or some kind of stress may be but it is curable... u need to visit a physiotherapist for the treatment like IFT / US / hot pack... if the pain is muscular as u told u have pain on the left side of the spine u can also go for dry needling technique to relieve the tensed muscle with a help of sterile needle that has been inserted intramuscularly...get well soon take care
Next Steps
Visit a physiotherapist and a dry needling expert
Health Tips
Hot fermentation at home is a must
Few days of rest is also mandary
Do not bend ur back
Do not lift heavy weights
Kindly go for few blood test like
calciumvitamin dvitamin b12 as if there ranges are deranged then u need to have those supplement medications for sometime