Well, you could have a muscle strain or pull? Also the lower back where you describe is heavily attached to your hamstrings. I had a low back issue and the medical massage therapist I went to released it through my hamstrings. Sounds weird but it is all connected.
I'd try this --- take ibuprofen. It's a pain reliever and reduces inflammation. I'd do gentle stretching. You can use a heating pad and/or alternate with an ice pack. Have you ever seen or heard of menthol patches? They can come in size large or xl which is probably what you need. Icy Hot is a brand, salan pas is another brand. You get them at the drug store. Put that on and it can be very helpful. There is a natural product called arnica. These are all US names so you may need to google for what it is called where you are. But I'm sure they are all available as they are quite common. This is in lieu of going to the doctor which would be best. Massage is awesome, highly believe it that. But don't forget stretching too.
Give it a week or so and if you are still in pain, you may need to bite the financial bullet and see someone about it. Maybe the orthopedic doctor family member would be willing to help you. Let us know how you are doing!
You are welcome. How are you doing now? Any better?