Dizziness

I'm 35w3d. I went to the doctor last Wednesday and they told me everything looked great. Since then though I've had 3 dizzy spells where I've felt like the world around me was literally spinning. Once was in the shower and I actually had to lean on the wall to keep from falling. The other two happened while I was seated. Has anyone dealt with this? I'm going to call my doctor tomorrow but I wanted to hear others experiences.

Oh and I have not been dizzy at all throughout the whole pregnancy, this just started