If you feel nose pain after shooting for a while, it is not a random thing. The LCD and eyepiece on most DSLRs are perfectly aligned to maximize nose-smashing.
Redditor lilgreenrosetta explains how to push the eye-piece just a little bit backwards so it sits comfortably against your eye.
Here are some pictures showing how he assembled the pieces together.
“After doing some research I’ve found two simple, cheap add-ons that can make life a little better, at least for the Nikon user. They are the DK-17M Magnifying Eyepiece, and the DK-19 Rubber Eyecup. The magnifying eyepiece gives the viewfinder a 1.2x magnification and also protrudes a little bit further from the body than the original, which is good. The eyecup makes the whole thing sit much more comfortably against your eye and, also very important, blocks out stray light.”#
If you are a Canon shooter some DSLRs supper the Canon EP-EX15 Eyepiece Extender which does a similar job (and costs a third of the price).
Tip: upgrade your DSLR viewfinder [reddit]