@Cleverporpoise
I feel for you, I'm having to battle with constipation too which tends to lead to me being impacted. It's always worse when I'm pregnant though. I do suffer with my bowels anyway (even as a kid) and my GP refers to it as a lazy bowel. The only thing I've found what works is movicol, I'm going to start having a sachet everyday again just to keep things moving. It doesn't taste great but you can add dilute juice - you do need to remember to drink water to make sure it works. It's never a painful movement either, I've found some meds can be.
The thing with constipation is that once it gets bad and you are really blocked up, when you do finally go your digestive system is still sluggish after the movement. So you need to continue taking movicol as a 'maintenance' dose for at least a week to get your bowels back up to speed - so to say! This was my mistake for years, I'd finally go and think I'm fine and then I'd be back to being constipated again. Doctors recommend talking half dosages i.e 1.5 sachets per day in pregnancy rather than the standard 3 and gradually increasing if needed. Annoyingly with movicol, everyone's tolerance is different so you have to find the right amount what works for you. It could be worth chatting with your GP about amounts and frequency though as it sounds like you are really struggling.
You can buy movicol over the counter as it's safe to use in pregnancy or doctors can prescribe it but they tend to give you Laxido or CosmoCol. I would definitely recommend asking your GP about it if other meds they are prescribing aren't working. I'm surprised they haven't gave you it tbh.
Lactulose and suppositories don't work for me either. My GP did also prescribe me docusate sodium capsules in my last pregnancy to take alongside the movicol on a night and that helped when I was talking ondansetron. It's awful, I remember stopping taking Ondansetron at points throughout the first pregnancy because I couldn't cope with the constipation. I was literally in tears crying, in agony on toilet and went weeks without going. Then it would result in me being bed ridden again and throwing up so I'd have to take ondansetron again. It's an awful cycle. Baths helped and I bought a cheap Sitz bath from eBay or Amazon as well.
Just one other thing (sorry for the long post), be careful about your fibre intake - if you are backed up and drinking prune juice etc, it's great it's working but if your body isn't used to that much fibre - you can overload and that can also block you up ironically.
I do hope you feel better soon though, it is truly awful x