I have a 3 year old boy and just had a DD 2 months ago. It was very difficult juggling both kids. My DH was only home for the first week, my parents had scheduled a vacation the following week which didn't leave me with much support. I did have a friend stop by occasionally. The best advide I can give you is to breathe and know that it will get better. There were times they were both crying.. and then I would start to cry as well. It was about a month before DS seemed to adjust and so did I. Unfortunately the bonding with DD is still not where it should be.
I try to get my DS on an activity or watching tv, having a snack when I need to feed DD, and I let him know mommy needs some time with the baby. When she sleeps I do an activity with him. Everyday isn't perfect but I find managing my time, leaves them both taken care of and hopefully I get some time to have lunch or just sit while he plays. I hope this helps. Hang in there.