Please help me w/nursing diagnosis!

Oh, please someone help me. I've spent HOURS on my IW. I called my instructor to ask if my nursing diagnosis sounded correct. She didn't call me back until after I had already finished. Initially, I chose "Acute pain r/t surgical incision." She said that it would be better to say "Acute pain r/t knowledge deficit." Is that an ok way to write a diagnosis? This pt was not using the PCA correctly and was constantly rating her pain at 8/10 without pushing her button. I had to do a lot of teaching about the PCA and reassure her that she would not OD herself if she pushed it many times.