Yes - you need to take a Vit D mega dose in order to get your levels up as soon as possible. You are considered to have low Vit D, even by normal (non-MS) standards. In the UK, doctors think a normal level for non MSers should be at least 50nmol/L, so your GP should agree to a mega dose.
To give you some idea, my original Vit D level was 23nmol/L. My GP prescribed a mega dose of 480,000iu over 8 weeks, which took my Vit D to 173nmol/L. Since then, I have been supplementing with 10,000iu per day. I am not sure where my Vit D level is at the moment.
Once you have had a mega dose, you should be able to keep your levels up by daily supplementation. Professor Jelinek recommends a Vit D level of around 150 - 200nmol/L.
Hope this helps. Vit D is not just about fatigue - you are more likely to relapse if your Vit D is low.