I know dilation doesn't mean labor BUT..

I went today at 37 weeks and 5 days. I'm currently 3.5cm dilated and 50-60% effaced. I've been having horrible back pain and pressure in my butt which is why he wanted to check me, he BELIEVES I could be in early labor but makes no guarantees. What do you guys think?? How long we're you at 3.5 centimeters before going into labor? By the way this is my second baby. My water broke at 37 weeks 3 days with my daughter at 3cm dilated!