What Causes Difficulty In Breathing After Hip Replacement Surgery?

I had a hip replacment,11 weeks ago .About 3 weeks ago I found it hard to breath like I had a flu and being asthmatic started on predisone but this time I didn't respond to ventolin neb either and ended up in hosp. A chest x-ray showed R eventration of the hemidiaphram. I cannot breath at night and sit up could my phrenic nerve have been damaged. I used to have 1 pillow now I have 3 and still cant breath properly.