I'll try my best! The hormones released during pregnancy are designed to loosen the ligaments which surround all of our joints to accommodate a growing baby and also to prepare for birth. That's why we have to be careful lifting anything because it' far easier to hurt yourself. In SPD it seems that the ligaments loosen too much so you end up with excessive movement in the pelvic joints.
There is a joint at the front of the pelvis, the pubic symphysis and two joints at the back, the sacroiliac joints where your pelvis connects to your spine just a bit higher than your tail bone. These all loosen naturally but when the gaps become too wide in the joints it makes the pelvis quite unstable and painful. You often get crunching and grinding of the joints too.
The risk is if you repeatedly stretch these joints too far it becomes harder for the body to re-align them after the birth when the hormones return to normal. So you have to try and protect the pelvis as much as possible. Bearing in mind it takes all the weight and pressure from the top half of your body but also pressure upwards through your legs, it deals with balance when sitting and standing still or moving. It does a lot of work in a day!
So if you are just sore at the front it's only SPD but if you are sore at the back too then it's technically called pelvic girdle pain, although most will refer to it still as SPD. The pain might also move to your groin area and feel like it's in your hips, or moving down into the thigh a bit. There's also some round ligaments which is more inside the pelvis where your pelvic floor muscles are, connected to the pelvis, these can be affected too.
Ideally after birth when your hormones return to normal so will the pelvic joints although sometimes this won't happen without more physio etc. It can take hours or years to improve, so if you can look after yourself now then it's much better in the longer term.
Oh and there's no harm getting a cleaner to do some of the heavy work (my cleaner is my OH

) And it might help you to prioritise so you can keep doing the stuff you want to do, rather than need to. And I still drive but only short distances as my right side is worse than my left so constantly moving from accelerator to brake can be quite uncomfortable!