The occasional presence of blood mixed with mucus in the snot is not a cause for alarm. Most likely the nose was picked by him inadvertently or intentionally. Use paracetamol
, keep him loosely swaddled in cotton clothes, give him Triaminic cough
syrup for his acute symptoms and try and feed him with small quantities of easily digested food and nutritive liquids like a chocolate milk shake, fruit shakes, etc.