K.L.
J. -
I had this problem with my son at 4 months old, too. He preferred his mom over his dad. I brought this issue up with my pediatrician. The doctor said that my son could sense his mother, the main caretaker. He can smell the food and is used to the holding positions. My son had to learn to be with his father. You can try to get him acquainted with daddy by having daddy hold and play with the baby when the baby is in a good mood at small doses with mom present. Then slowly, increase the time and mom can slowly be absent. Hope this helps!
Good luck!
K