about 6-7 weeks it started for me, although I never threw up, I just felt like i was going to all the time! And its died down now, that probably happened about 11 weeks
Mine started right from about 5 weeks... Then got really bad pretty quickly. Now, at 7.5 weeks, it seems to be a liiiitle better, with weekly acupuncture and 200mg of Vitamin B6 daily.
With both my pregnancies it kicked in at 6 weeks. With DD it was a LOT worse than this one and lasted a lot longer. My aunty was pregnant not long after I got preg with DD and she had no m/s at all, ever (not fair! ), so yep, everyone is different, doesn't even seem to run in the family.
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