Dizzy, lightheaded, etc

Just wondering if any of you get this way. When I work out especially or bend over and stand up quickly, I get very lightheaded and dizzy. I see stars and just feel pretty faint. I take all of my vitamins and get in plenty of water and protein, so wondering if this is normal? I am going to call my doctor, but just wondering if any of you guys are going through this too. I have been pretty tired lately too, like taking naps in the afternoons, something I have never done...even after having a newborn!! I just get real tired after doing little work. I know my period should be coming in the next week or two, but this is the first month I have felt this way. Oh, what about potassium? I have seen a lot of mention of it, but not sure what we should be doing to get it in. Anyway, sorry to ramble but hoping you guys can help let me know if this is happening to you as well Thanks!! Erica