Hooray for your doctor testing your levels! I'm so glad to see this starting. My midwife tested mine as part of a normal screening. I wish SO much someone would have done this for me 10 years ago. I believe if I had corrected my levels that I probably wouldn't have been diagnosed with multiple sclerosis in 2005.
I am taking 4,000 IU a day and trying to raise my levels. I have done a TON of research by reading studies and information published on Vitamin D. It is completely safe and needed by our bodies. There is NO good way to get enough Vitamin D via diet. Our bodies are meant to get Vitamin D from the sun but sometimes the sun isn't enough. Some of us seem to be genetically predisposed to not get what we need from the sun (and you really do have to be out in the strong UVB rays for quite a while to get enough as it is.) I was taking 1,000 to 2,000 IU and getting sunlight and my levels only raised a little. So now I'm taking more to get it in the normal range.
My guess is that if your doctor suggested 4,000 IU that you are severely deficient. According to the latest research, this may put you at a greater risk for all kinds of cancers and autoimmune diseases.
I'd take 4,000 IU a day without question and have levels retested after six months. Try to get to the upper range of normal, not bare minimum (e.g. 32 is still too low, 80-90 is best!)
If you are looking for a nice pure supplement, this is the brand I use with my toddler (it comes in 400 IU, 1,000 IU and 2,000 IU sizes - you could use 2 drops of the 2,000 IU) http://www.vitacost.com/Carlson-Vitamin-D-Drops
Ingredients: Vitamin D3 (Cholecalciferol), Fractionated Coconut Oil.
Free Of Sugar, Soy, Corn, Wheat, Gluten, Artificial Coloring, or Preservatives.
This site is good for some basic Vitamin D info (and they offer an at-home test for Vitamin D through ZRT labs.)http://www.vitamindcouncil.org
ETA: Oh, I forgot to add that you want to take D3 (Cholecalciferol) NOT the synthetic plant-based D2 (Ergocalciferol)