I know where you're coming from with not wanting to take painkillers. I'm still only taking paracetamol when I really need it or know that I have to do something that will pain me a lot. I'm hoping for a natural birth with minimal painrelief too.
Oh an make sure you mention to the midwives that you have the SPD/PGP when you're going into labor. Especially if you have an epidural, they have to be very careful not to overstretch things and do permanent damage to your hips. There are certain positions you should be advised to avoid or should be recommended to you.
I know it's not always easy to follow all the guidelines and sometimes you can adapt them to your own as well. I, for example can still squat and find it actually helps it, while recommendations are not to. But then I can definitely not do anything "one legged" and with a big belly it is just so tempting to try to push things with your leg instead of bending and picking them up...
When I initially started having groin pains I found this website great for information:
https://www.pelvicpartnership.org.uk/
Also, one of the things my osteopath does (and some of the hands on physios as well) is massaging your outer bottocks and your outer upper thigh area. It releases the tension. I found that great and even though my husband doesn't get the spots exactly right, it still helps if he does it in between (and I checked with my osteopath, she was happy for him to do it at home as he can't do any damage if I make sure it's not painful. It's just like a deep muscle massage).
So here comes my attempt in describing what we do:
Lie on your side, have the lower leg stretched out and the upper one bend, resting on the ground. (Just a comfy lying-on-your-side position pretty much)
To start or if you're unsure about the ellbow let your partner massage your lower back, hip and thigh area with his hand and palm (he can be quite firm). Even that will feel nice...
If you want test for tender spots in your soft tissue (not the bony parts of you hip) yourself by pressing into the muscle areas with your hand or fist. When you find a tender or tense spot get him to bend his arm and put his elbow on that exact spot. Get him to apply pressure to the spot (so that you feel it but never that it's too painful, he can "lean" into you) let him apply the pressure for about 20-30 seconds. Then let him release it gently and rub the area for a moment.
Do the other side after you finished with the first.
I find it particularly helpful before going to bed after a long day, so that the stretched muscles have time to loosed overnight...
Hope you'll get relief soon!
(There are usually about 3 or 4 spots that I can find are sore. One is on your upper outer bottom pretty much underneath your hip bones, one is on my outer thigh, pretty much where you bend and on the lower outer side of the thigh...).
If you ever had sciatic pain, most spots are pretty much along that "line of pain" that you get with sciatica...