Often subtle. "soft signs" are often the only early clues that a newborn is ill. Not feeding as usual, not awakening for normal feeds, irritability, seemingly minor fevers, slightly increased breathing or heart rate, poor feeding, increased spitting up or "just not acting right" are all possible signs of newborn illness that could even be serious. Call your doc right away if you suspect anything.
Irritability. Irritability, excessive sleeping or fever may be the only sign of babies illness. Please call if your babies rectal temperature is over 100.4 and discuss the signs with the doctor.