Low achy pelvic pain

Ju
I'm 18+2 weeks and a FTM and sometimes get an achy pain low in my pelvic and lower back. Its not constant but I get in every few days or so and it seems to hurt more when I strain going #2. Does anyone else get this? I know its probably just my uterus growing and what not but I just want to make sure its normal. Thank you ladies.