Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today.
How long has he has these signs?
What injection was given specifically?
How much blood are you seeing? A scant amount, a spoonful, or more?
Can he keep water down?
Are his gums pink or pale/white? Moist or sticky?
If you press on his belly, any discomfort, tenderness, or tensing?
Could he have eaten something he should not have (ie bones, toys, plants, chemicals, etc)?