I had the same thing when my 4 yr old was a little guy up until he was about 3. I went to my doctor and he perscribed zoloft with a very very small dose. I was apprehensive about being too zonked out on any medication to take care of my son, but the truth be told, I was zonked out from lack of sleep. I was apparently very anxious and had kicked into "super mommy" mode during the night and going through the motions as a zombie during the day. Every little thing, noise, light, or even the dog or cat walking through the room and I would be wide awake. My body is now reporgramed and I am no longer on zolft. Some people are funny about being on anti depressants, there is a certain stigma that goes along with the word depressant to new mothers. "I'm not depressed, I'm a new mother of a wonderful child"....but it's not the depression part, just the anxiety, and constantly running through your head "how long has it been since he last ate, diaper change, cry?", in short, worrying about being the best mother you can to your child. I would talk to your doctor, he may even have suggestions that are not perscription related.
Hope all goes well!!
Jennifer