Did you even do anything in general without noticing it? It could also be something she has done and she just can't bear to face you. However, shes your wife, she should listen to you if you absolutely did nothing wrong to your knowing.
You should not forget that youre the man in the house, take charge and tell her that you want to know what shes been up to or whats bothering her.
Can't really help since your post lacks evidence, but hopefully that she isnt screwing around with other guys. If she is, leave her.