I hate to be a party pooper, but cinnamon is also an allergen for many people. Many kids, bakers exposed to it at work, and increasingly women in general, experience contact dermatitis or worse from cinnamon (I've read of women who can't walk through airports because of Cinnabon!). My 1 yr old daughter broke out in hives on her face everytime she had food with cinnamon in it, but she outgrew the allergy. If you're nursing, I'd be cautious about ingesting too much, just in case it's getting in your milk. And be careful not to sprinkle any on your babies!
Regarding the weight loss, are you nursing this child more than the others? If the weight loss is that surprising, you might have to have your thyroid checked. Thyroid imbalances are common after pregnancy. Then again, with 3 kids, you probably don't find time to eat!