it sounds like the dizziness could be from a number of things:
1) you say you haven't eaten much because of nausea, are you drinking? we get quite a bit of liquid from the food we eat, if you aren't eating you should at minimum be drinking 2 liters. dehydration can cause dizziness because your blood becomes thickened due to a lack of fluid. this makes your blood volume, and therefore blood pressure lower and pumping it up to your brain becomes a challenge.
2) you have recently started a new medication. does this new med have any effects on blood pressure or is dizziness listed as a side effect?
3) a new relapse. dizziness is often a symptom of MS activity
if the dizziness is to the point that you are falling or having trouble taking care of yourself its time to get yourself into the docs office ASAP. the doc is the one who can sort this out for you. sorry this is happening