I could have written your post OP.
My first pregnancy was a mixture of extreme sickness, illness and panic so I didnt enjoy it. My DD was early so I didn't get a due date and I has terrible PND.
My second pregnancy was a disaster from start to finish with loads of problems and a premature baby who spent 3 weeks on a life support machine. I was seriously messed up and had terrible PND.
I was desperate for a third baby so I could 'do it properly' and 'have all the things I missed out on'. I really wanted 'closure' after the second DD's birth and felt strongly that a third child would be my chance to really enjoy pregnancy and babyhood.
I then had three misacarriages in a row and started to think I'd mucked the whole thing up!
My third (surviving) pregnancy was a disaster with a problem diagnosed at 6 weeks and hundreds of scans and hospital appointments. However, I loved it. I really relished every moment and spent hours rubbing my bump and being excited.
My third birth was amazing - a lovely water birth in a birthing centre and home again in a couple of hours.
I have LOVED LOVED LOVED everything this time round and have been PND free which is amazing. I can actually breathe this time round and I'm really enjoying it. It's bloody hard work with three but, for me, it's really given me closure and made our whole family hugely happy.
I fully appreciate that this is just my personal experience and could so easily have gone the other way.
I'm so lucky to have got the closure I so desperately needed but if things had gone wrong, or the PND had returned, it couldve finished me off!
I find the easiest way to know if you should have another baby is to sit everyone round the tea table. Then look around the table; in your heart is there anyone missing? If you have a deep gut feeling that someone is missing, have another. If not, there's your answer!
Best of luck whatever you decide,
(my kids are 6, 3, 4 months)