Ok so I put it all into the title! LOL!
My 4 and half month old baby girl has spent two days being VERY fussy. She is usually an extremely happy joyful baby. Her stools have been green for a while and the seem even darker. They have a bit of mucus and a bit of blood. She is exclusively breast fed.
This all started yesterday morning. We gave her vitamin D drops for the first time. DH fed her a bottle of expressed breast milk a while later (I was out of the house) and she threw it all up and then some and then some more. She hasn't thrown up at all since. But that was the start.
She is just so unhappy! Pooping frequently but not a whole ton. She was a bit lethargic yesterday but not so much today. She is nursing more often than usual too.
What do you think I might be dealing with here. Is it the vitamin D (she didn't get any today)? Is it a food issue (as in food I'm eating?)
My first thought, upon reading the title and the first bit, is foremilk/hindmilk imbalance. I still think that's a very possible problem if the green poop has been a problem for a while. I think it would be well worth taking steps to correct a possible foremilk/hindmilk imbalance (block feeding, massaging the breast to encourage the milk ejection reflex aka letdown earlier, pumping on the side baby is not nursing on to encourage the MER, etc.). Oversupply is also a possibility.
It does sound like the vit D drops may have had an additional effect. IMO, I wouldn't bother with the drops. For one, your baby is under 6 months and unless your baby has been tested and shown to have low vit D levels, I would advise against direct oral supplements. ANYTHING a baby gets besides breastmilk affects their gut negatively, not just solids. This could be the case here (and you cannot always see the signs, EVERYTHING negatively affects their guts, it's just that it is sometimes obvious and other times is not at all). Instead, if it is a concern for you, I would advise you to take vit D supplements yourself. Vit D has been shown to increase in milk levels if mother increases her own intake (via vit D rich foods and/or supplements). This way your baby will get increased vit D but without the harm to her gut.
I would be almost sure it is the drops. It is a very common reaction.
(Have you looked at Kellymom on supplements for babies? Do you live in Northern Canda and wear a burka? What, you don't, maybe you don't need the drops... Seriously, read the study to see the source of the recommendations.)
Green poop is also common when the bf'ing mom takes an iron supplement.
This was one of the first signs of my son's dairy intolerance.
I'm not sure what brand of Vit D you are using - but I think the Carlson drops are based in a coconut oil. It could be a reaction to the drops. OR - could be a virus. Or too much foremilk like PP mentioned.
In any case - mucous & blood indicates GI irritation. If you nurse on demand - finishing first side first - may clear up the situation. Hugs