"Mother's intuition" is more than a cliché (and it applies to dads, too!). It's a powerful tool that can help you raise your baby. You know your baby best, so you can be an especially keen judge when it comes to changes in your baby's condition.
As Benjamin Spock famously wrote in the first line of his classic 1946 book Baby and Child Care, "Trust yourself. You know more than you think you do." If you feel something's not quite right about your baby's health, development, or general well-being, don't be too quick to dismiss such feelings. Many a parent has been ahead of the medical community in detecting the first signs of a problem, whether it's the beginnings of an illness even before fever appears or the presence of an undiagnosed disorder that's causing behavioral changes or a developmental delay.
So what should you do? Heed your instincts. Write down your observations. Don't hesitate to consult with your baby's doctor. And if you still don't feel convinced, persist until you get an answer that satisfies you.
Don't worry if you make mistakes or suspect a problem when there isn't one once in a while – everyone does. Between recognizing gut feelings and learning from experience, you'll figure out how to do what's right for your baby.