Heavy back pain blood result shows Vitamin D3 deficiency

Navitha
I am at 20 weeks 2 days. I was suffering from heavy back pain for past few days. Doctor advised me to check vit d3. I got the result today. Terribly low value of vitamin. What to do.. I am afraid of vitamin deficiency affects my baby. Can anyone suggest some foods that contains vitamin D3. And also I have a little amount of vaginal discharge ( clear color ) with pain in vagina. Is this common or not ??