J hit all the sleep regressions a week early, must be because he was a week late. His birthday is the middle of the month so I usually get a bit of warning from the earlier babies. As Sophia said I didn't know anything about sleep regressions with my older two so ignorance was bliss. On the other hand with J being such a rubbish sleeper it's good to know the insane nights are temporary when you're bang in the middle of them. When DS2 was this age he had been sharing a room with DS1 for over a year so there was no way we had the same ishoos with him as with J. I would have described DS2 as a bad sleeper but that's probably more because he gets up in the night quite often, even now. I would say he didn't reliably stay in bed at night until he was about six years old.
J's sleep has been transformed since he went almost dairy free. He does still wake at night but is more likely to self settle and he doesn't do the crying for an hour, body rigid, tummy gurgling, needs Calpol sessions any more. I was so chuffed with myself at managing to get dairy-free potato cakes for yesterday's breakfast then DH went and fried them in butter. 
In his defence he tried to fry them in bacon grease but they were sticking so he transferred then into the mushroom plan where he was using butter. So J had an inadvertent dairy challenge yesterday. He wouldn't eat any lunch then was quite grumpy by dinner time so it's possible there was a reaction but he slept really well. What a change from a couple of weeks ago!