Should I get help or wait?

I'm 21 weeks and 3 days. My backs been hurting for about a week but just mildly. But today it started getting really severe and I can feel my uterus tightening and it gets really hard. The pain is also transferring to my right leg and I'm kinda of freaking out. I'm a Ftm. My ob office is closed and there is a on call but just for emergencies and I'm not sure if it's an emergency or not . I just don't know and I'm so overwhelmed . Any advice? Also my next appointment is next thrusday with my ob