Please do not accept that physios advice. There is things that can be done to help ease severe Spd, in terms of manual therapy. It will not get rid of the pain, but it will help ease it. You need to try and find a chiropractor or osteopath who work with pregnant ladies.
I have had Severe Spd with both my pregnancies. Last time it started at 12 (ish) weeks, and by 27 weeks I was in complete agony. This was when I was signed off and started seeing my chiropractor. She honestly kept me mobile, as without her I am sure I would have ended up in a wheelchair. This time I started seeing her at 7 weeks pregnant (pain started at about 6 weeks), am now nearly 34, and have only just been signed off work, and only just started wearing my pelvic support band.
Take a look other pelvic partnership website too. They have lots of good info on there too.
Take care
Em x