Pus is what comes out when something infected is finally opened, so it is read as hidden resentment or pain being released. Unpleasant as it is, it points to cleansing.
Does the traditional reading fit your dream, or did it mean something else to you?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.