Hi Charlotte and blimey, you certainly have a lot going on in your life!
I’m a 72 year old guy and no medic so not best placed to answer some of your questions but:
On mobility issues - I’m 72 and was diagnosed some 19 years ago. For years (8-10) I didn’t have any mobility issues at all, that changed slowly to not being able to walk for more than 30-40 minutes to my current situation of needing a stick and, for longer walks, a mobility scooter. I still walk around the house unaided , cook etc etc
On mental health- depression and anxiety are more frequent in people with MS than in the wider population but by no means do everyone with MS experience either. My thinking is that a diagnosis of MS is itself enough to get anyone down , some treatments can affect mental health and , if I were you I would give myself a bit of time to let thing settle down and to allow yourself an opportunity to come to terms with it all. In my case I’ve got myself some counselling from time to time to help work through things.
Like many others I also take Citalopram- been on it so long now that it’s pretty much just part of life.
On cognitive issues- this is just my guess but I wouldn’t be surprised if what you are experiencing is a result of a combination of everything, perhaps including Tyruko ( have a check). In my case I struggle with thinking etc when it gets warm and for 1-2 days after my weekly injection of Avonex.
On the positive side, at 72 and after 19 years of MS I don’t think my cognitive abilities are too bad. I test them every now and then through an online test on Food For the Brain and there is a harder , more thorough test on The Great British Intelligence Test run by Imperial College London .
Finally, have a look at the Website of Overcoming MS ( living well with MS) which in addition to advice and guidance on diet and exercise also has sessions on Mindfulness which is good for general mental health, calming the mind etc.