ETA: I just realised how long this is

I won’t be offended if you don’t read just looking for some advice or perspective please!
I work in a very physical job by way of visiting patients at home in inner city London - therefore I walk betweens patients and generally see 4-5 a day. This can regularly mean I’m walking 20,000-30,000 steps just between the hours of 8:30-12/1. There are only two of us who do this specific job and although my line manager is supportive I’m not sure she understands the physicality of my job and how tiring it is. She has told me to “take it easy” and I am not being pressured to keep up with the same amount of work I was at all. But I am happy, while I can, to continue doing home visits.
I have an office to work from in the afternoons and as a base to leave equipment that I may need and don’t want to carry to each home. However, without warning one of the senior admin managers has decided that she now wants my office to work from 2 days a week and wants me to vacate it immediately. Now I add she had not told me or my line manager this directly - I heard from another colleague.
There are no plans for where I am to have a desk (and we do not hot desk). Desk space is also at a premium and clinicians who are seeing patients on site regularly turn up to have no space to see them never mind me just needing a desk for admin work.
I am unsure if senior admin lady knows I am pregnant (I told my line manager i did not mind senior management knowing). She also has another office full time on a sister site (20 min walk away).
Am I right to be so put out by this? I am worried that I will have nowhere to rest after a tiring morning and am certain that I must have the right to discuss this with occ health /HR? I do intend to discuss this with senior manager and let her know I am pregnant - I do not need my office if she wants it but she does have to find me an alternative.
My line manager is basically just saying “she says she needs the office back” and nothing else.
I’ve actually put in my notice as I’m leaving in 12 weeks but it seems like since I’ve said I’m pregnant and leaving they do not care what so ever and it’s really stressing me out.