You should take 5000iu a day, unless you weigh more than 150lbs. You should do this for 8 weeks and then retest your levels. We promote maintaining a healthy level of 50ng/ml. If at 8 weeks your level is less than 50ng/ml, then you would need to take more.
I recommend you read http://www.vitamindcouncil.org/about-vitamin-d/vitamin-d-and-other-vitamins-and-minerals/. It is very important.
If you have health issues at this time, let me know because the recommendation, for how much to take, might change.