Nursing more frequently and sleeping less is a sign of one of two things--either your little one is in a growth spurt or your milk supply is low. Make sure you are eating healthy, drinking plenty of fluids (Drink a minimum of 8-12 ounces of fluids every time you nurse.),and get plenty of rest.
At four months, you are typically going back to work, trying to accomplish more around the house, etc. You may need to take better care of yourself. Make sure you are getting enough rest. The old saying about sleeping when the baby sleeps is very true. Go to bed earlier at night or try to take an afternoon nap. If you are doing too much around the house ask your hubby to help more so that you get more rest. Take care of you--it is the key to a happy, healthy baby while you are nursing.