When does back labor start?

I'm only 17+3 and have a history of back problems. But tonight it is causing vomiting. And the visiting caused me to wet myself. It is located in my lower right side only. Feels like a spasm that won't go away. It is horrible when I move, lay or even breathe deep at all. Has anyone experienced something like this so early? I took a home pH level urine test and it was 6.0 (neutral) so I don't think it is a kidney stone. I'm going to retest with my urine first thing in the morning. If it doesn't let up I'll go get checked. Thanks in advance.