So sympathise, I had with all 3 pgs, earlier and worse each time, on crutches last time.
Unfortunately as others have said nothing will make it go away except giving birth ( which weirdly doesn't seem to hurt anymore due to the spd, in fact early labour was quite "nice" for me as the spd pain went away for first time in months )
You can do things to ease it which in my experience are:
Support belt - helps a fair bit
Physio - helps but not huge amount
Cranial osteopathy - helps a lot, but effects are short lived, few days then you need another appt and this is pricey
Memory foam mattress or topper - my other top tip, really helped ease it at night
what really helps if course is anti inflammatories which of course you are not supposed to take in pregnancy as not been tested. Check with doctor if there is anything that you can take if gets really bad. I used voltarol gel locally on my si joints in desperation a few times last pg and it really helped ( and gallons of it first few days after birth ). Not medically recommended though,
As others have said, it usually improves v quickly after the birth.