OK wll I only have 2 but we ummed and ahhd over a 3rd for a long time after DS2 was born.
My cousin recently had her third. She's an excellent mummy, really hands on, very patient but even she says 'STICK AT TWO' haha. It's early days for her though, her DD is only 3 months old so she (hopefully!) will feel differently when things calm down a bit.
For now she just says she feels like she's just firefighting the whole time. One of them is always about to blow up about something and she's there in the thick of it trying to breast feed a baby and the older 2 are acting up and fighting more because of this.
Like I say, it's early days and it will get better but don't underestimate the level of chaos a baby bring upon the older siblings...especially as thy get older and can remember a time before the little one arrived.
She's really struggling with jealousy and her boys are constantly pushing boundaries now.
Also, it's already been said but she feels overwhelmed going out with all three of them. Suddenly there aren't enough hands. Even when her DP is there, they're always always outnumbered. This is a huge problem while they are young and need a lot of physical help and maneovering!
We decided to stick at two for many reasons. I still find it hard with 2 most days (admittedly it's harder right now because DS1 is obviously off school for summer holidays and entertaining the two of them on my own while DH is at work is torture sometimes).
I still feel like I would always want 'just one more' but at some point you have to stop and do what is best for your mental health and the well being of your existing children.
If you can look at it objectively and honestly think you are ready and want to go ahead then absolutely you should have another child. BUT if it's like me where I was kind of just mourning DS2 growing up and kind of knowing I'd never have another then you need to be realistic about what you and DP can actually handle.
3 children is difficult whatever the age gaps. It's a huge strain to never be able to have 'one each'! One on one time for children of three is so much more difficult.
I was one of three and whilst my mum was great, we were all seen as the 'collective kids'. We weren't really given time to be individuals or allowed to have an opinion or chose what we did or what days out we had because it was just so hectic for my parents and caused too many arguments between us all! My parents were just all consumed by just cooking for us, cleaning up, managing clubs, sorting disagreements, walking my brother to Scouts, picking my sister up from Brownies, next night me at swimming classes, bedtimes etc etc.
I had a good childhood don't get me wrong but I sometimes look back and feel sorry for my mum! It must have been so hard. One on one time was none existent so we didn't really know her on any level other than the cook, the cleaner, the handholder accross the road. Sadly I don't think she really 'knew' us either. We were just 'the kids'. I appreciate many people manage and somehow factor in one on one time but it just become so much harder when you're out numbered.
Anyway, this has become rather negative hasn't it?! Sorry, I am sure it would be lovely at times but for me it just all seems like 'hard work' and not enough time to enjoy the rewards. Good luck with whatever you decide. Plenty of families manage 3 and many more children. Perhaps I am just a lightweight!