I agree with previous posters that you should have a chat with your doctor. As our profession is an isolated one for the most part, I can only imagine that can add to depressive symptoms as well. When you spend your day caring for others, we have to remember that self-care is equally important.

I started my daycare back in March to be at home with my Daughter after a bad daycare experience (that, and I returned to my pre-mat leave job for 5 months and it had changed substantially and was HORRIBLE, and I was struggling there). I am finding I am loving the day to day of operating a daycare, however when I start thinking long term of what I have done to my career (my previous career) and what will I do after this (when my kids are in school) I start to get really down and depressed. What helps me come back from it is reminding myself that no matter what the future holds, I will never regret this time at home with my daughter. It is such a gift me to be the one who gets to be there for all her milestones and all the precious moments I may otherwise be missing.
Don't let that crazy lady make you forget why you're doing this too. Things will start getting better soon!