Aww Layla, it does sound like SPD hun, so sorry.
You've described exactly how I felt, intense pressure, the 'kicked' feeling, the pain when walking, and the feeling that you need to hold onto something when you walk. I ended up on crutches and really struggled to walk, but that was acute. I hope you don't have it that bad hun as it is awful.

In the back of my mind is always the thought that I may get it worse with the next pregnancy, as I have no idea how I'm going to walk on crutches whilst pushing a pushchair!
Go and see your mw Layla, she can refer to to physio and they can get you a support belt which will help.