Sever lower back pain and achy legs throbbing in upper right arm. what should i do my vitamin d level is only 15 please respond asap thanks ?

Check it out: I would tat 5-6000 iu/day vitamin D for low D. But see your doc for the rest.

Two questions: You want your vitamin D level above 30. Usual dose is cholecalciferol 50,000 units once weekly for about 12 weeks. Back pain and extremity pain are something else. It is often difficult to find a reason. Check with your doc if it does not resolve spontaneously within about a few days.