Balancing being a parent to an infant and pre-teen

Recently I gave birth to a beautiful baby boy, who ironically enough shares his birthday with our 12 year old daughter. For the majority of my daughter's life I was a single mother and spent all of my time focusing the attention on her. When my husband and I met she did a really good job of adapting to sharing her time with me in turn they have created a very close Bond. Recently my husband adopted her and she was over the moon to change her last name to his, so we all have the same last name now.

Our son is now a week and a half old and I find myself feeling awful for not being able to spend more time with our daughter. I have been trying my very best to balance taking care of an infant and breastfeeding (time consuming) and spending time with her but I already feel like I am failing. I ask her at least daily of she is doing OK and if she needs anything from me and she always says she is fine. I just miss our girl time already, and hope it comes back before she becomes a teen and doesn't want anything to do with me. On the other hand, I want to enjoy my son during this time as well.

Does anyone have advice/experience they can share with me?