The 4 month sleep regression hit Holly too. She STTN from 8 weeks to about 4 months, and has never STTN since. This week she's getting a little better, but she keeps waking up at 5am to play. I think some babies get over it pretty quickly, but for some it can go on for months (Holly is 9 months). FX you're one of the lucky ones! x x
ps, I agree with Emma - weaning doesn't help in the slightest...