I had SPD from 8 weeks and sciatica on top of that in my 3rd trimester - for the last 6 weeks or so I was on crutches, and with an active preschooler already it made life pretty challenging. That said, I found a combination of things helpful in managing it - family / friends for support, regular physio, swimming when I could, and occasional acupuncture and osteopathy as well.
Yes it went away after baby was born, although not straight away - maybe a good 4 months before things started to feel more "normal".
It didn't affect my labour or birth at all as I was focused on managing through my contractions etc, and DD2 was in too much of a hurry anyway (labour was less than 2hrs).
HTH