Take
Vitamin D supplement on weekly basis for 8 weeks. Then check Vitamin D levels if it's within the normal range you can stop it as increase in Vitamin D beyond its normal range can toxicity like bone pain, stiffness etc.
Cod
liver oil you can take for first 3 months then keep a gap and then you can start taking it.
Sit in the sun for 15-20 minutes thrice a week. Take fish meat egg etc and take food fortified with vitamin d.
Next Steps
Consult under practo in case of emergency!