Since you never saw a doctor, how do you know its a torn/strained muscle? Disc injuries actually present themselves as pain in the low back and buttocks. A stabbing or searing pain is the typical presentation. Its known as referred pain. So you need to go see a doctor that specializes in core and back problems ASAP. If you are lucky its a muscle injury. If its a disc injury, then each time you returned to activity you actually made the problem worse.
Your description of the ever lengthening recovery periods is right in line with a low back disc problem.
Unfortunately disc injuries need lots of time and rest to heal. Fortunately, if you catch them early and let them heal, most resolve themselves completely and you can eventually return to action with little worry. However if you keep stressing it whiles its still injured you will eventually cause a serious problem, probably a fragmentation or even a full herniation. Once that happens, you will be out of commission for a long time and it will never recover to 100%.
So its best to get it checked out now. An x-ray can not really show soft tissue injuries, but it can highlight if there is a thinning of the space between vertebrae. This is a preliminary indication that something is wrong with a disc or discs. The doctor may then have an MRI done to see if there is actual disc damage. Since you are recovering fairly quickly, a good doc will treat you conservatively with lots of rest, some pain meds and anit-inflammatories and eventually some physical therapy. If it doesn't resolve within 2-3 months, or the pain begins to radiate further down into your leg, more aggressive treatments may be called for.
Bottom line, get it checked out and follow your doctor's orders. There are no shortcuts when it comes to healing a recurring back problem and trying to power through it guarantees an eventual catastrophic event. I speak from personal (and very painful) experience.
-k-
