Dear Alok,
The most effective way to increase the
vitamin D level is to get sunlight in the morning hours (between 8am to 11am). Only 15 minutes exposure with bare minimum clothes will be most effective. 2-3 times a week will is sufficient.
For diet, you have eggs (egg yolks), soyamilk, mushrooms, fish (Tuna, Salamon). Feel free to consult me if have further queries :)
Next Steps
Follow the above advice for 15 days and then let me know.