DC1 was just...screamed A LOT basically, no medical cause identified, she gradually grew out of it. She's nearly 4 and still a very intense child that tries to argue and negotiate over absolutely everything, has frequent huge screaming meltdowns (every single morning is a meltdown for ages before she decides to get ready and have breakfast, for example) etc so I can believe it was just her personality...on the plus side she has generally been a decent sleeper, although she started regularly waking in the night once she hit 3.
We hoped DC2 would be a bit more settled. The first 3 months or so he was a fairly typical newborn apart from the lack of proper naps, but as I was breastfeeding I would just stick him back on the breast all the time so it was manageable, he didn't cry that much, he was attached to me most the time but that was doable. However he 'woke up' around 3/4 months and he older he gets the more he cries. He's 6 months and he's somewhat better if we are out and about (same with DC1) but he spends most of each day crying now and just like with DC1 some of it is clearly overtiredness given he doesn't nap properly but other times I have no idea what is wrong or how to help. He is also not an amazing sleeper either (could be worse but he still has between 1 and 3 feeds a night and now frequently won't settle after and spends like 30 mins sessions of crying in the middle of the night etc). I'm just exhausted and miserable, I feel like there must be something I do wrong to have two babies both just upset all the time and why can't I soothe them and make them happy or make them nap? :(