Hi and welcome,
I'm not sure your question has landed in the right community or not, Multiple Sclerosis is not something you can take "I have been on it awhile" or cause "blisters" on your tongue, MS is a neurological condition...
It's possible you are experiencing an allergic reaction as allergy is a common cause, the other common causes of blisters on the tongue are trauma and viral......you could see your GP but tongue blisters are not generally a sign of something serious.
Hope that helps.....JJ