I suddenly can't write or speak as quickly as I used to be able to - is this ms?

Not quite. Any sudden change in neurological function should be immediately evaluated in a hospital setting. There are a number of causes of sudden change in language including stroke, migraine, infections, and yes, ms. You need an urgent evaluation to look for the underlying cause.+.
Unlikely. Although these could be symptoms of ms it is unlikely. Evaluation by a neurologist should determine the cause of your speaking and writing difficulties.
Not necessarily. You are describing issues which could be due to a host of causes, even including depression, anxiety, and stress. Best you have your doctor evaluate and treat the underlying cause. MS would not be the most common explanation for your symptoms.