With a level that low most doctors treat by giving 50,000iu once a week BUT it is much better to take Vitamin D on a daily basis so that would equal about 8000iu a day. They should wait 8 weeks and then retest your levels to “make sure” they have risen enough. Your goal should be to maintain a level of 50ng/ml(125nmol/l). This is a “healthy” level. At levels below 40ng/ml your risk for cancer and autoimmune disease rises “dramatically”.
After being treated with a higher amount, that should give you a level over 50ng/ml. After that than most people weighing an average of 150lbs should take 5000iu a day to be able to maintain a level of 50ng/ml. If you weigh more, you have to take more.
If you take the 8000iu for 8 weeks and do not make it near 50, then there is a problem and you should come back and tell me.
I encourage everyone to read http://www.vitamindcouncil.org/about-vitamin-d/vitamin-d-and-other-vitamins-and-minerals/.
If you are battling any kind of condition or disease, you may also want or need to take more Vitamin D!