We use Lollipop pop n gro size 2 here too. I find it depends on what I stuff them with. They do have a tendency to get a bit too untucked around the poppers. They really need a third popper in the middle to hold them properly in my opinion. Saying that I find if I am using my less floppy inserts the pocket does behave (at least until the insert is wet and the nappy needs changed and then he looks like droopy drawers
) It might be worth playing around with different inserts. I guess you could also get someone to put in a third popper in the middle if all else fails.
In terms of PGP I can highly recommend going to an osteopath. My pelvis had got out of alignment and the muscles on one side had got really tight to try and compensate and my osteopath loosened things up, got things into better alignment and got me moving with much less pain. I still have it a bit now (LO almost 2) and I needed physio to try and address the muscle imbalance. Don't just accept the support belt and crutches, there is better help out there.