Hi Zeppy, I'd assumed you were already out of hospital and home, though I think The Real MC suggested you're still in hospital. I'm going to continue assuming you're home, but if you're not, obviously ask a nurse to check your rash and advise on pain.
The painkillers you're on are pretty strong, but I wouldn't have said it's abnormal for you to still be in pain despite taking them this soon after surgery. Don't think you're not strong just because you need painkillers - you've been through a lot physically and emotionally; physical pain tires us emotionally as well, and I know how it feels to just want to be comfortable and sleep well for once. The painkillers you're on can lead to tolerance however, which means they become less effective over time.
It might be a good idea to see your doctor just for a check-up. Not necessarily your surgeon or a specialist, just your GP (I'm not sure of the names where you are - maybe family doctor?). They could have a look at the rash and make sure you're on a good plan for pain relief. If you need to be on painkillers for a while, a few more weeks at least, they may be able to prescribe some that don't have the tolerance problem. They're usually not as strong, but as you heal and your pain decreases, you will probably be able to come off the ones you're taking currently.
Cushions and hot water bottles may help you sleep. The warmth of hot water bottles helps your muscles relax, though if you're getting night sweats that may not be what you want. You may want to check your temperature regularly. Fevers are pretty common after major surgery. They're often not serious but, again, it may be something you want to check with a doctor if it is high.
My last surgery I was on painkillers for a few weeks, however, I take painkillers regularly anyway, so although I stopped the extra, stronger ones then, when I did stop I was not without pain relief entirely. And to be honest I'd have stayed on longer if the doctors had let me, even though I knew I'd risk addiction if I'd stayed on them much longer. I have had major surgeries in the past where I just wasn't allowed pain relief, for various reasons. It took quite a few weeks before I was comfortable enough to sleep well. It's always worse at night and I look as the first night I sleep well as a milestone in recovery. If you're having trouble with pain, you could also ask your doctor for something to help you sleep through the pain rather than just targeting the pain itself; I've found that to be a very effective approach.