My 20m girl was coughing throughout the whole of last night. And in btw, I could hear wheezing sounds when she breathed. What could be the reasons for the wheezing sounds? She doesn't has blocked nose not runny nose.

She may be wheezing as her airways could be getting narrowed due to the infection. It would be safer to bring her to your doctor to assess as children this young cannot tell you they are having breathing difficulties and it is not as obvious as in adults.