Is she egg bound?

[Tia Z.]

I've read everything on the internet but I want to hear from you about symptoms of a duck being egg bound. I'm not sure if mine is, underneath the base of her tail feathers appears to be swollen but that is the only thing I see that is different than the male. She's been looking around building nests in places for a few weeks now. She sits there for an hour or two but no eggs. She also stopped flying up to the roof at night. Other than that, she has a healthy appetite, I haven't noticed any straining, and her feathers aren't fluffed up. Could it just be that she's preparing to lay an egg and it's not ready yet? I'm nervous!