Walking at 32weeks

I went on a walk (3 blocks) with my husband tonight and was feeling a TON of pressure down in my lower abdomen, where my son's head is. To the point where it was almost painful to walk and felt like my stomach was getting tight. Is this normal at 32 weeks? What is it??  I see my doc on Tuesday so I'll ask her then but also wanted to ask here. I'm fine now that I am sitting again.