Afternoon nap nightmare

I. Need. Help! 3 week old daughter refuses to sleep in the afternoon. She's a great sleeper at night and in the morning, but refuses to sleep in the pm. I will feed her and walk her around the house until she is totally passed out, put her down, and she wakes up 20 min later, screaming. And nighttime is crazy. So far I've been trying to put her to sleep for almost two hours. I'm so frustrated and tired. What works for you? What else can I try?