Back Spasms, Not Getting Larger, Not Hurting, May Be Oblique Muscle Tear.
Thanks for posting your query.
From your description it seems you have got your muscle pulled with a small bleeding inside causing a hematoma formation.
A direct examination and investigations like MRI scan are the best to find out the extent of soft tissue injuries do take 2-4 weeks for healing if adequate rest is provided to the affected muscles.
Doing a hot fomentation and taking mild pain killers like ibuprofen will help you. For intermittent muscle tensing, you can get an appropriate muscle relaxant prescribed from your doctor.
I hope this answers your query effectively.
In case you have additional questions or doubts, you can forward them to me, and I shall be glad to help you out.
Please accept my answer in case you do not have further queries.
Wishing you good health.
Regards.
Dr. Praveen Tayal.