Hi OP,
Sorry to hear you are in so much pain. I have had SPD in my last two pregnancies, last one was the worst. Had to be signed off from 21 weeks and was housebound for the rest of it. Had crutches to get to my midwife appt and didn't leave the house otherwise so I know how isolating, debilitating and mentally draining it can be. From a personal point too, I struggled to bond with baby in the womb as every ounce of my attention was on how much pain I was in. Similar to you, the midwife told me it was "normal"...
I tell you the rest of my story not to scare you but just to help you avoid what I have been through - I had to get induced at 38 weeks due to GD, baby did not want to come out and got stuck in my birth canal for 2 hours. I had the epidural and spent this entire time in high stirrups - midwives weren't concerned re my SPD and said so long as I couldn't feel pain I'd be ok 
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After the birth I struggled to walk for 6 weeks. 2 years later I am still in physio and have learned a lot about recovery and how to help yourself with the condition - obviously mine is a major horror story BUT I just want to share some of the things that have worked for me and learned on my journey.
I have seen advice on here to do pregnancy yoga - I have been told this is a big no no by several physics. The relaxin is stretching your muscles so without any strengthening work, stretching them more with yoga can aggravate the condition.
Rest rest and rest some more. Get signed off for a few weeks and see how you do. Resting meant I could move around the house at least. At the same time you need to maintain some level of activity but do not go beyond your current means. If you can only walk 100m pain free then maintain that and try the exercises physio gives you on top and slowly build up.
Get to the 121 physio and do whatever homework they set you. It may take a while to feel the effects or notice a difference but you will get there. They will give you exercises specific to how your pelvis is - what suits one doesn't always suit all with SPD. Avoid any internet classes until physio have told you your limitations - it is hard to go from being young and active to doing simple and gentle "exercises" I did and do feel like an old granny making tiny movements instead of bouncing away in a gym class but you don't want to make anything worse. Internet classes won't take account of your condition and it is far too tempting to try and keep up with those glowing instructors.
Use a tennis ball to massage sore points. Put the ball between yourself and a wall when standing and slowly jiggle around - it won't cure you but it may get rid of some pain.
Sleep with a pillow or pillows between your knees and feet so they are equal. Brace your core when turning and use arms to help you get up before swinging feet off the bed- gently and slowly!
If you can't afford an osteopath, look up osteo schools nearby - the downside is you will have several students looking at you in your undies but it is a fraction of the cost, about £18 per treatment in central London so hopefully cheaper outside.
See the GP or go to triage - They can give painkillers. I only ever took them 4 times but it was 4 nights where I got some much needed sleep and you really sound like you need a break.
My current physio recommends icing the area even when not sore as a preventative measure. Either soak a pad or fill a condom with water, freeze and then wrap it in a clean tea towel before placing next to your pelvic bone/SI joint - very attractive! I've not done this yet out of sheer embarrassment as never home alone 😳. Alternate ice and heat where necessary.
Most of all, be kind to yourself. It will get better and take each day as it comes. Right now that 40 week finish line seems impossible but you will get there and you can do this. Adjusting expectations from what you normally do to what you can do when do restricted is mentally very hard, or was in my experience. Take each win where you can, take as much help as is offered and spend as much time in the bath as possible! Look after yourself and all the best 