Are you having any symptoms or do you have any health problems? (This could influence what I tell you or change what I say below.)
Most doctors treat a deficiency that is that low with about 8000-10,000iu of D3 (not D2) A DAY. You do this for 8 weeks and then retest. This should put your level at 50ng/ml or higher. We recommend maintaining a minimum level of 50ng/ml. At levels below 40ng/ml your risk for cancer and autoimmune disease rises “dramatically”.
As long as your level ends up higher than 50ng/ml, after that you can probably go to a maintenance dosage of 5000iu a day. This is if you weigh an average of 150lbs. If you weigh more, you have to take more. If for example you take 8000iu and in 8 weeks your level is 35ng/ml then you need to take more. If for example your level is 50ng/ml then you will have to keep taking the amount you are taking. If for example it ends up being 80ng/ml then you can try the 5000iu as maintenance.
I highly recommend reading http://www.vitamindcouncil.org/about-vitamin-d/vitamin-d-and-other-vitamins-and-minerals/. It is very important. Pay close attention to magnesium. If your diet does not contain enough magnesium, then taking Vitamin D can cause symptoms. So if you get ANY symptoms that you already do not have, come back and tell me. You level is so low that you may even need to take calcium supplements.
Let me know if you have any more questions!