I had the same thing except I go outside frequently. My level was ~13. After taking vitamin D 5 days a week for a month, it was brought my levels up to 27. Another month later it was like 42. After that, it was at 60. I'm suppose to keep taking vitamin D supplements because for some reason my skin just doesn't synthesize sunlight very well.
I usually spend 2-4 hours outside every day, so sometimes you just don't get enough from the sun.
My DR recommended I take one pill of vitamin D (10,000 i.u). a day for 5 days a week and then nothing on the weekends.. Go see your DRs and see what they recommend because it may be different.