This can become post-natal depression.
I was like you when I got home. My hubby took leave to be by my side to watch over me until I could get a better grip over myself and my emotions.
I think you're feeling tired and overwhelmed by the transition into motherhood.
It would help to share your feelings with people who're encouraging, be it friends or your husband. It's ok to tear or cry.
I also suggest that you get some rest - sleep. And also hydrate yourself. Dehydration and fatigue affects appetite.
Try to think of happy thoughts. My hubby even bought me a happy meal from Macs.
Is there anyone helping you out at home with your baby and chores? Are you breastfeeding?