and Red cells in blood suggest infection like say dysentery
. This can be confirmed by stool culture. In babies less than 6 months.... there is risk of infection spreading to blood. Most doctors will prefer to start antibiotics in such cases. This all can be related to new feeds if they too preceed the onset of loose stools.
Milk bases feeds may need to be stopped if the stool reports presence of sugar and acidic pH.
You may read details about loose stools and diarrhea