What to do if i was recently diagnosed with severe vitamin d deficiency. what could be causing this?

Many things: Vitamin d can be ingested (in milk/ supplements) and can be created in your skin via sun exposure. The latter is becoming less common as most of us use sunscreen! vit d plays a vital role in bone density and woman are at increased risk for osteoporosis. Peak bone density is at age 35. Got milk? Increase milk intake, use supplements as necessary, and increase weight bearing exercise to build bone.

Lack of sun & supps: Virtually all americans become deficient in vit d in the winter months if they don't supplement. It is impossible for us to produce vit d from sun in the fall & winter (unless you live in the deep south) as the sun is never high enough in the sky for uvb rays to reach us. Most adults need 5-8, 000 iu of vit d3 to achieve optimal levels. It is best to take vit a & k with d as they work in synergy.