I'm useless for the first 5 or 6 hours after I wake up (which these days could be ANY time frankly!), getting gradually better later during the day, and generally feeling fine by bedtime, so that I too tend to stay up late just to get a few hours of productivity into my day. If I try to get to sleep at a 'normal' time, it doesn't help, because even if I'm not itching I generally can't sleep unless I'm properly tired. So nowadays I tend to just sleep whenever I'm tired and keep on working whenever I can.
So far, everybody seems to have the opposite pattern to SaveMe! IMO, the probable explanation is: we can't sleep properly, and in some respect sleep is actually exhausting for our bodies. There's the phrase "it's like your body is running a marathon every night while you're asleep", which seems to fit - something to do with cortisol and cytokines failing to switch off their activity, I think (?)
SaveMe, I think I've mentioned this to you before, but my guess for your pattern is that it might suggest some sort of chemical sensitivity, or some other kind of sensitivity. Such things can take years to track down, I'm afraid, but they make a big difference once you've figured out how it works. Although the flare-ups may seem random, I would tend to suspect they aren't, really. I suggest: try to identify where you are, what you are doing, where you are sitting/lying etc, at the time when things start to go wrong during the evening. If it's always happening when you're in bed, then the bed itself is an obvious candidate. I haven't been able to sleep in a bed for a few years now - I sleep on a leather sofa, which is very far from ideal still, but a massive improvement from when I was still trying to sleep in beds and going through one mattress after another, one set of bedding after another, and just getting worse. Whenever I try (or am obliged) to try sleeping in a bed again, it's straight back to the old nightmarish situation: probably one of my biggest ambitions for my life would be to be able to sleep in a bed again one day!