Are you getting any help for your SPD?
I had it in both pregnancies; first time round midwives were very dismissive and I eventually got a couple of physio appointments in the last few weeks including a girdle/support belt thing that went around my hips and held the together which provided some relief.
2nd time around, different area. Mentioned it to midwife early on again (started around 12-14 weeks both times). She was sympathetic and immediately Referred me to physio who started appts a couple of weeks later. Got physio to knock me back into correct alignment, exercises and support belts (different as I got bigger), fortnightly sessions and although it hurt it didn't get anywhere near as bad as it did first time around.
I didn't need to walk very far nor was I at work which I'm sure would have exacerbated it further. If I had been, they would have given me crutches or a wheelchair - would having either of those help you? Even if you just had one at work it would help to remind others of your limitations and hopefully give you some relief.
And if you don't have a support belt - is there a friendly physio at work that could sort one out for you? My midwife was reluctant to refer me to the physio to get one on the basis of 'they don't work for everyone'. The physio however said they work for a hugely significant number of people (greater than 95%) and should always be tried as even if they don't help they can also stop it from getting any worse.
I was one of the ones that was helped by them and whist I was pregnant it was first thing I did in the morning - put it on. Choice between that and teeth brushing it would win every time if I was short of time - that's how important it became. (not a choice I needed to make very often thank goodness!)
Hope you get all the sorts of support you need sorted out very soon!