Fiona, I am sorry you are having a bad time. MS is good at that - even when you have had it for a little while and are getting on OK, it has the power to make everything just suddenly feel a bit hopeless, just by grinding a person down. Plus, of course, its ability to take the legs from under you - literally or otherwise - without warning.
It sounds as though you feel your treatment plan is just drifting a bit. That can happen as years go by, particularly when things start going a bit awry (I remember that feeling well from my own experience…). Does the recent MRI offer an opportunity to sit down with the neurologist for a proper, gloves off review of where you are, how your MS is behaving, and what your options look like for treatment etc? There is always guesswork with MS, but it can help at least to have the specialist opinion to help guide your thinking.
Low mood: that is usually something that the doctors are better at fixing than they are at fixing MS, quite honestly. If you have not already spoken to the GP about feeling low and tearful and hopeless, please think about doing do. Might as well fix the things that can be fixed. I know that, when things are really rough, it can be hard to imagine ever being in a better place. Try to let yourself believe that there are medications and therapies that can help you to see life in colour again.
Good luck with it all.