Back Probelm While Running

Patient: When I start running I am fine, but as I get up to 2-3 miles I get this tight spasm feeling in the the lower right back. As I keep running it starts to pain slightly, but it’s not major. Then my lower right back-hip area starts to feel like it is rising up and arching in. Then It starts to feel as if my right leg is shorter than my left, and it feels so awkward to run. This has been going on for over a month. So when this happens I try to straighten my posture or maybe hunch over a little so my hip won’t rise upward, but it doesn’t help. I have to stop even though I’m not tired. Is my back out of alignment? Is it a muscle sprain or spasm? I really need to get back into running. This is the best way I could describe it.