Reduced sensation “down there” is a very common MS symptom - for both men and women.
If you are having, or have recently had, a relapse, it may return eventually - mine always has. I don’t think I’m quite as responsive as I once was - but then again, at nearly 47, I’m not sure what I could realistically expect now anyway!
I’m sure it’s not in your mind, and I think it’s pretty unlikely to be your medication, given that it’s such a common MS problem.
For men, viagra sometimes helps, but there is no specific treatment aimed at women - I sometimes feel it’s not viewed as important for us. I’ve never even been asked if I was OK that way, even though I’ve been asked about toiletting etc. As I’m not in a relationship at the mo, I suppose it isn’t that high on my list of priorities, but it would be nice if it wasn’t just assumed to be irrelevant, if the patient happens to be female. Or maybe it’s only if she’s female and past 40?
All I can suggest is patience - both on the part of your bf (success can still be possible with perseverance and a willingness to experiment), and yourself - over the long term - hoping it’s just a temporary thing.
I didn’t wake up one morning and it was suddenly all better, but gradually, over many months, I noticed sensation was almost back to normal. Your body will heal it if it can, but unfortunately it’s not easy to predict how long it might take, or how complete it will be.