" It isn't down to luck it is routine."
Hmm, yes, I had a friend who said that about her first two: all about the routine, that's why they slept so well, no bad sleep associations, all through my hard work, careful tweaking of feeding and nap patterns, fantastic parenting, etc. Until she got child #3, the Sleep Resister, and realized that you can help it along a bit, but mostly, it is just luck.
I had no routine whatsoever, cared not a whit about rods for my own back, bad habits, "setting a pattern", etc., child the first was a terrible sleeper, child the second mostly slept through from 8 weeks (with blips for teething and developmental spurts). I also think full night weaning at 14 weeks is a bad idea, a lot of babies genuinely do need milk at night for both calories and comfort even if you've tanked them up during the day and they're not "supposed to".
Agree with the PPs who said it's a (horrible) storm to be weathered. Here's a good post about the 4 month sleep regression:
askmoxie.org/blog/2013/05/should-you-sleep-train-your-4-month-old.html
(I also like askmoxie.org/blog/2005/12/quick_and_dirty.html)
Also if you're having difficulty dropping off between feeds, have you tried magnesium supplements? A lot of new mums are mildly magnesium deficient and one of the symptoms is insomnia, I found my ability to conk out after feeds greatly improved when I started taking it.