Hi there
Is it possible you just wiped the 18 month regression from your mind with your other two? I only have 1 child and I still can remember the 18 month regression (which started at 16 months here) but I know I don't feel the full strength of just how hard it was when I look back on it. At the time it seems all consuming, a couple of years later it's like a blip on the time line of development.
It's really common for babies this age to have the sleep regression, it's a pretty huge developmental leap at the half birthday, it can also show itself as SA, whining, fussing, and general irritability and poor humour. then there's teething on top of all that which can go on and on for an age before the teeth finally cut. Language development too...a real whole heap of stuff that LOs are going through at this point.
The general advice is to stick with your routine, respond to the SA with as much mummy time and understanding as possible, medicate for teeth if it helps, and wait it out. It will pass.
There's a support thread if you'd like the chance to chat and commiserate with other mums going through the same?
18 month sleep regression support thread-part 3