i don't think you'd notice much symptom-wise through taking vit d3, it's more about keeping your immune system in line among its many other important functions, and in the ms relevant studies i've seen it's preventive, lowers risk of developing ms, and can help reduce relapse rates.
your vitamin D supplement is likely either vitamin D2 or vitamin D3 if you read the label carefully. does it say ergocholecalciferol or cholecalciferol? you want cholecalciferol (D3).
sun-exposed human skin can sythesize 10,000 IU vitamin d3 in half an hour. research on vit d3 suggests an adult uses 4000 IU per day, so if you are supplementing 2000IU then you'd need to ensure your dietary intake is 2000IU per day for maintaining current serum levels. if you want to get your levels higher, you need to take more.
paulmur probably means 20,000 IU/d. in my opinion that's a bit much to be taking daily in the long term, but in the short term, with bloodwork, it's fine. just have to be sure not to go over 250 nmol/L.
depending on the status of other nutrients in your body, your ability to absorb d3 will vary. i found that once i identified and fixed a zinc deficiency, i could no longer megadose d3 in the same way without risking going above 250 nmol/L D3 in serum, which is dangerous. i got a new syringe so that i can eke out 10,000IU drops, whereas before the smallest drop i could get was 25,000IU (which i would take 1x every week or so in general).
what all do you deal with symptom wise, v, and what other supplements are in your regimen other than vit D?