I'm a bit nervous don't know how will I know when this pain means going in to the hospital I'm 36…

I'm a bit nervous don't know how will I know when this pain means going in to the hospital I'm 36 weeks pregnant and I spent all day in bed due to pain on my lower back and pelvis I couldn't even move right now I'm having not as much pain so I took a shower and I'm in bed again how can I know when is time?