I'm having trouble with my high E string on my guitar.?

It's hard to explain, but there's something wrong with my guitar. When I tune it, on the high E string, the notes aren't what they should be. It's mainly any note after the 12th fret, but it happens on any fret. If you played the 13th fret on the string, it sounds the same as the 12th should do, then the 14th fret makes the note the 13th should make, then the 15th fret makes the notes the 14th should make etc. Also, I can't play any harmonics on the string. However, I can't play a harmonic (natural harmonic) on the 12th fret, but I can on the 13th fret. I've tried re-doing the string but it did nothing. Any suggestions, I'm really stuck (if it helps, my guitar is an Epiphone Dot). Thanks in advance.