Pip went thru that when she was six months old, and it was my fault. I feed her some people food and the seasoning on it was most likely what did it. Believe me, there was absolutely no more so called 'treats' of human food after that! It was totally my fault!
The worst of it hit her during the night, I was up and down with her, too. By morning, she pooping bright red blood, and vomiting. Got her to the vet, she told me another 2 hours or so, she'd have been beyond saving. They put her on IV, and kept her for 4 1/2 days.
I hope your baby is fine now.
