Vit d treatment course if for 3 months once a week. After 3 months you have to stop it for a month and get your vit d levels tested. If they are in normal range you don't have to worry about further treatment. Also weakness can be due to various causes long term
vitamin d can be one of them. You will need to consult with a doctore regarding which one of the causes could be yours depending upon your clinical findings and history
Next Steps
In case the range is still low after 4 months you have to repeat another 3 months treatment followed by 1month rest then repeat vit d test
Health Tips
It's really helpful to have food sources with high levels of
vitamin d as they are helpful in your long term