Desperate to walk more

I'm 30 weeks and for the past month or so I've had real problems with walking, which is my main way of getting anywhere. I've a pain/pressure which feels like it's in my bladder or possibly the top of my pelvis which I only really feel when walking and a little when I get in awkward positions at home. Midwives mentioned UTI or SPD but I've got no other common symptoms of either and the pain is really specific to walking (or running- which is out of the question).

I'm otherwise fit and healthy - swimming regularly and doing other fitness things - but the lack of being able to walk is starting to really affect me. It's not just the physical side but it's making me feel both vulnerable and dependent, which I'm really struggling with.

Anyone experienced anything like this? Am I just going to have to grin and bear it for the next two months?