I too was recently diagnosed with Vit D deficiency hence my interest in your post. I can't imagine much fluctuations taking place over weeks. I can imagine it takes a long time for anything like that to take place, probably several months. I have to take Vitamin D capsules = 2,000IU daily to bring me back up to what I need each day. I am never out in the morning sun, which is when we get the benefits of the sun, and because I do get out for a few minutes or more of an afternoon I thought I was going okay. Apparently that wasn't the case with me. When we consider how we are advised to cover up, especially down here in Oz, to prevent melanomas and other skin cancers, we have no chance of getting sufficient Vitamin D naturally from the sun. When you were told how low your Vit D measurement was, were you prescribed a replacement supplement? You should have been.