20 weeks, can’t stand for long at all...

I went to Walmart yesterday and was there for maybe 30 minutes. I kept feeling really dizzy and light headed and can’t stand for long without loosing my breath, I kept having to sit down and couldn’t think straight. My whole body starts to heat up and feel tingly. This happened the day before when I was at my doctors office. Is this normal? Anything I can do to help this? 😣