MS is a strange thing, but even if it is a true relapse, it will no doubt go back to normal as your other arm did in January. I had several little events like this in the early stages of my disease, but the were soon gone and forgotten, which was probably just as well at the time: getting on for twenty years ago.
On the other hand it might be a pseudo-relapse, as here:
This can occur even when you have started antibiotics totally, especially in the first six months of treatment. When are you actually starting them? When nearly three years ago, I started, David had not then thought through the use of NAC so I started straight off on doxycycline, full dose, followed by roxithromycin two to three weeks later, when we managed to obtain it. In a way, I think this still has its advantages, although both Stratton and David now seem to build people up more gradually.
Keep us informed and if you are worried about something the best thing is to maybe send me an email or PM because I am trying to develop the art of not reading all the posts on both sites every day, so I might miss something as I did last week.