I try to take vitamins regularly, but sometimes I'll go weeks or months without them. When this happens, I'm usually relatively healthy while not taking them, but I always develope a cold and sinus infection when I start taking them again. Does anyone know why this is happening? The first couple of times I just chalked it up to coincidence, but it's happened at least 5 different times. I don't normally get sick often (though I do have troubles with allergies from time to time), and it seems strange that vitamins (most recently pre-natal vitamins) would make me sick.