Sad about last baby

I have a son who is 2, and just had my daughter 3 weeks ago. My husband and I always said two kids was perfect, and I feel so fortunate to have one of each. Lately, however, I am feeling so sad that this is my last baby... Anyone else? I am trying to enjoy her while she is tiny, but everything is reminding me of how fast it all went with my son, and how this is my last little one.