There is fixing deficiency and then there is "hyper dozing". Also lot of it is seasonal, northern hemisphere is entering summer so there should be plenty of sun light even with short exposure to light.
I don't think exposure to light is enough to overcome an actual deficiency. When you're exposed to light you get kind of a huge dose, until you get a tan. Then your skin won't produce much more for a while.
You're right about overdoing it. There is such a thing as vitamin D poisioning. I think it draws calcium out of your bones or something. On the other hand, not enough vitamin D is bad for your bones too.
Fortunately, there are tests for vitamin D. If you think you have a problem with it, you ought to get a test.
