fainting spells

So I'm 32w5d and the last 2 days I've had 3 really close fainting spells without any common denominators. One was right after finishing lunch. The last one was tonight at our birthing class... I got very pale and clammy and the nurse had me lay down and prop up my legs. My next appointment is Wednesday so ill ask the doctor about it then but I'm really getting concerned. Has anyone else ever experienced something like this and if so what did your doctor say about it?