Need advice

So I’m almost 25 weeks pregnant and when I’m at work standing for long periods of time hurts my back a lot and slowly makes its way to my stomach. That pain goes away when I get home and rest but today I’m still having like a pulling pain in the lower part of my stomach every now and then. It’s scaring me and bothering me because I don’t know what it is. This is also my first pregnancy. I need some help on what could possibly be wrong or going on.