My son was older, about 28 months at the time, but about a month before his little sister was born, his behavior took a major turn for the worse. At the time I was working full-time too and hated spending my evenings at home with an irritable child. I know he sensed things were about to change, and he felt out of control. We started giving him a lot more choices and that seemed to help a little. Kids are very intuitive and pick up on all kinds of things. We tried to keep our evenings very calm and when possible, spend as much time as a threesome doing the things he enjoyed the most--jumping on the trampoline (mommy just sat up there, no jumping for me) and taking walks in the evenings after dinner, playing soccer etc. The other thing my son started doing at this time was demanding mommy do everything from baths to storytime to playing with toys, I had to be present. We knew he was feeling insecure and this was part of the need to feel in control, so for the most part we just humored him. It did seem to help him feel better. Just try to be as understanding as possible and reassure him. Be prepared for the first few months after the baby comes home to be very difficult for your son (and you), but after aabout 3 months it becomes much easier. Don't be afraid to ask for help and in the evenings when daddy gets home, hand off that baby and spend some quality one on one time with your son. We used my daughter's morning nap everyday to play games (it was torture playing candyland everyday, but he really enjoyed it) and it was quality one on one time without interruption. Also, don't be afraid to ask for help from friends/family.