Thanks for all these additional details.
I am sorry to hear about your problem and I know how worrisome this situation can be for you but hopefully, we can resolve this.
It sounds like a Muscle strain or a pinched nerve.
You can follow these measures to get free from such symptoms-
1. You can apply ice packs on your back for 15 minutes and can be repeated 3-4 times a day.
2. Stretching exercises for your low back can help you feel better and may help to relieve nerve root compression.
3. You can start with OTC Ibuprofen and can be taken in a dosage of 400 mg thrice a day.
5. Muscle relaxants would also be helpful for your condition.
6. Please take frequent breaks, while doing work. After every half hour, make sure that you move out of your chair for a few minutes.
Do gentle massage with muscle relaxant ointment and apply warm compresses with a heating pad on the back.
Refresh Your Posture. Apply analgesic gel such as Bengay ultra-strength. It is available as OTC.
Do gentle stretching and gentle exercises.
You can take help from a physical therapist. Physical therapy includes various modalities like - Short wave diathermy, Infrared, and Wax therapy, these will help you a lot.
Please follow suggestions, as we discussed and you would get good results.
Hope I have been able to clarify the situation for you and helped in resolving your query.
Please let me know if you have any additional questions or if you want to discuss this further.
Get well soon!