I'm on pregabalin and I've definitely put on weight too but in my case it's not just because of the pregabalin, although it's certainly not helped!! If you don't think the pregabalin is helping you then ask to change over to something different. Speak with your nurse/GP.
The 'desert' mouth feeling I know only too well. I use Salivix Pastilles, a natural salivary stimulant which my GP prescribes for me. There are other options available which he said I can try if these don't help. I also suck sugar mints too.
Up until probably about September time I was gluten free, I don't know why I suddenly reverted back to eating non gluten but I did and it's not helped matters . Although I noticed no difference to my ms it did keep my weight down and I felt better about myself. I had more confidence. Definitely.
Diet - as in what we eat - does make a difference. If you're famished are you eating enough? Or enough of the right things? A good all round healthy diet is the way to go (in my opinion).
This last year or so my confidence levels took a major nosedive - for all sorts of reasons - and part of the end result of that was that I started to doubt myself in all aspects of my life, including my job. I know I'm good at my job and I have very understanding & supportive employers & colleagues but still I felt as though I just wasn't 'giving' enough and that I wasn't quite 'good' enough. In my heart of hearts I know that's just not true but it didn't stop me feeling the way I felt.
I'm feeling a bit better about things now, so I am getting there but it's not always easy.
I think your first port of call should be your nurse or GP. Tell them you're not feeling well, see what changes can be made to your medcations. That alone can make a huge difference. If you're feeling better then maybe things at work will improve too.
If then you find that you do need adjustments made to your working hours etc then decide what will be best for you and then have a chat with your boss, but whatever you decide on make sure it's in your favour. Don't just go along with what he says!