Kinda sore...is this normal?

ali10

I'm almost 16 weeks and today for about the past hour, I have had mild discomfort in my lower tummy. For the past few days my stomach has really been filling out...up until now it has kinda been up and down...now def getting tighter and firmer. I know about RLP...which I have had a few of when I sneeze...but my discomfort today feels like the dull ache you get right before you start your period. Is this normal as the baby grows? I know it is active in there because I have been feeling it move constantly...I just want to make sure what I am feeling is normal!