Read the signs. It's possible for a child to have extraordinary skills as well as skills that are lacking. For example, an early reader may lack certain social skills. This is what is called in special education "doubly exceptional," meaning having a learning disability and being gifted at the same time.
Take notes. Jot down your observations when your child does something that you think is out of the ordinary, whether positive or negative. You might even want to take video of your child if the behavior is only observed in certain situations.
Talk about possible learning difficulties with your pediatrician. If there's any question in your mind about what you see in your child, then the first place to go is to your doctor. Explain your observations and show her your notes. If you're not satisfied with the doctor's observations, get a second opinion. Some pediatricians might want to look at home movies of your child to get a better understanding of the situation.
Get help for you and your child. Many states have a learning program for children diagnosed with learning difficulties. You may also want to join a support group so you have other understanding parents to lean on when you hit the rough spots of raising an exceptional child.
Know that every child is a unique creation and will have strengths and weaknesses just like all of mankind. Celebrate the strengths, work around the weaknesses and cherish the wonderful child that you've been blessed with.