Thankyou for the courage to write, first of all. I think mothers are expected to suck it up and enjoy parenting all the time. I have a seven year old and I struggled with depression as a teenager and currently deal with it. But when my seven year old was 8 months old, I really fell apart. My husband was a radio talk show host and I pulled him off the air to come home and help me. He never lets me forget it :)
I realized with my second I also had it. She is two now but it came on later. So the timing is not really important. Everyone is different. But I realized that because I grew up in a lot of violent behavior from my father, I was always outer directed, waiting to see what kind of a mood he was in when we got home from school, tiptoeing not to make him angry. It was all about him. And when my children were born, I felt outer directed again. Certainly not the same circumstances as growing up, but outer directed nonetheless. Once again I was in this trap of pleasing them first before myself. I still have trouble with taking care of myself because then the guilt kicks in, somehow I'm not this perfect person. I'm always rushing to get things done before the baby wakes up and that puts me into symptoms of depression.
I would highly suggest going to a Recovery Inc. meeting if you can find one. Google it to find their website and meeting locations. I don't like meds but I started taking rhodiola rosea, saint johns wort and then 5HTP at night. I got them at Wild Oats. They seem to work a little. But mostly support groups. I have spent many a time in Recovery Inc. balling my eyes out about struggling with what they call lowered feelings, which is depression and the recovery method is so profound.
I hope that helps. Just don't do it alone. Love has nothing to do with this. I know you love your kids. I do too. Also maybe some therapy. I was told early on that if I suffered from depression before kids, chances are it would rear its ugly head after kids.
Lots of love and support to you from me!