My daughter was very likely in an oblique position when I went into labour. She had been posterior/oblique (and breech!) most of 3rd tri. She turned head down at 34 weeks, but was still in a less than optimal position (head sort of at my left hip, bum up under my right rib cage). Lying to the left is better than lying to the right as they have less far to turn to get optimally positioned to descend during birth. As far as I know that's how she stayed. I had her naturally at 37+5. I think I had a pretty easy, straightforward, comfortable labour. It wasn't really painful, no back labour as far as I know (I have no idea what it's supposed to feel like, but I didn't obviously feel more discomfort in my back than anywhere else, so who knows?). The only more difficult part was that I did have a lengthy 2nd (pushing) stage of 4 hours, which is unusual and tiring, but not necessarily a bad thing. I suspect she was turning during this time (basically if they are posterior/oblique and to the right, they have to make like a full turn and a bit to come out facing the right way). I think that just took time, but it was fine. I was tired (like my legs were tired, because I was upright and squatting and walking around that whole time), but otherwise, it wasn't a bad thing. They monitored us periodically, but we were fine and they just let me get on with it at my request. She came out facing the right way, so she did turn. Honestly, it was no big deal and I wouldn't worry at all about doing it again. I did, however, practice natal hypnotherapy, so I was really relaxed and comfortable generally. I stayed upright and mobile (I was actually walking up and down the hallway in between pushes). And I used a TENS on my back from very early in labour (just when I was having strong period like cramps). Totally labour time was 11.5 hours (went from absolutely nothing to period pains to fully dilated in 7.5 hours, then the 4 hours of pushing).
If you do want to encourage better positioning, Spinning Babies recommends some exercises you can do (these helped when my daughter was breech). Being really careful about how you sit (not slouching, sitting on a birth ball as a chair, etc.). Also, see a chiropractor or osteopath to have your pelvis adjusted. Often a misalignment in the pelvis, especially if you have SPD, can cause baby just to not be able to get in the best position because there isn't enough space. So if you get it adjusted, it will open your pelvis up a bit more and might encourage a better position.