Is there anything I can do to ease lightheadedness in pregnancy?

I find it's particularly bad when standing/walking. I don't think I'm dehydrated, I've been drinking a lot of water and some lemonade too (such a lifesaver with nausea!) I don't think it's blood sugar, I've been eating small, frequent meals. I'm considering stopping by a pharmacy to test my blood pressure. I remember this being bad with my son and my OB recommended sitting/resting when I felt lightheaded. With a toddler, this is harder!

Any experience?