Pain in the *$$ & sides

So I was getting ready to go to a viewing with my mom over an hour away and when I sat on the toilet and peed, I had a pain go from the lower left side of my back all the way to the top of my thigh/below the left side of my bottom.

I could barely stand up from it. I was able to stand after about 20 seconds of this pain and carefully took a shower. I talked to DH and my mom after and both suggested instead of going to the viewing and standing around, I just sit home with my feet up (to which I will happily do, I hate viewings - who doesn't though).

So my question for you ladies, do you feel all kinds of things stretching and pulling? I have felt a pain on both sides of my belly (more outside like under my armpits between where my bra sits and my hip) for a couple of days now. I am not bleeding and up until the incident on the toilet the pains have felt like sore muscles. My mom (who was petite and went through 6 healthy pregnancies) says its just everything moving around and stretching to make room for the baby. Pre-pregnancy I was in physical therapy doing mostly pilates stuff to strengthen my lower back from a previous injury, and I had lost 12 pounds before conceiving, so I was in pretty good shape pre-baby, and I keep hearing that it is just my petite figure stretching out too.

My bump just "popped" a couple of weeks ago, so I agree with my mom and will talk to my doctor at my appointment on Thursday morning. But, I am wondering if anyone else has these feelings of just being sore some days? Or even shooting pain there (I think they call that the siatic nerve?)???