<s>[INST] I have swelling and pain to the touch in my lower back on the right side . It started two days ago quite suddenly and hasn't gone down. Inside of the swelling is a little smaller area that seems harder than the rest of the swelling area.  Please advise. [/INST] Hello, Thanks for your query.Sudden lower back ache could mean a spasm of the muscle due to some recent activity which had an impact on the back , as in lifting of weights, two wheeler rides, trauma/a fall etc these could also lead to temporary changes , which manifest with tenderness, swelling and a lower back pain. sometimes this could even mean an infection of the vertebra of the back you must be very careful. Minimize all your activities to possible extent, lie flat on your back on a hard mattress avoid soft cushions, take a pain killer and wait for a day, the swelling may come down. See a doctor preferably an Orthopedician for an examination, do not life heavy weights and ride two wheelers or even pillion. Follow the right posture for the back when at work . I do hope that you have found something helpful and I will be glad to answer any further query.Take care </s>