Hi Mat
Some comments about your fugue
mesure 1
The subject has a good ambitus (D to c) but sounds like a subject in G minor because, with a F# inside, it contains a modulation to Gm that is not resolved, I mean : followed by a come back to D m.
Your subject starts in Dm but finishes in Gm
A solution could be to make the subject longer. For instance, followed by F, E,D.
Using this solution, you could also replace F# by F.
mesure 2
The repons is not good because all the notes must not be the same than the subject a 4th highter,
some notes should be lowered by 2 semitones (mutation), or add few notes (c,Bb,A) so as to the repons ends in the tonality of D minor.
mesure 5
the 3rd voice enters here. it must be in the tonality of D minor; exactly the same notes than the subject mesure 1 but one octave lower.
Your 3rd voice starts in A minor and ends in Dm.
I miss time and your hand written score is not easy to read for me, so i stop analysing here.
Your music is nice, pleasant to hear, your counterpoint sounds good, but your music is not in the form of a classical fugue.
May I suggest you to look at :
http://en.wikipedia.org/wiki/Fugue
and practice the following method :
http://www.wikihow.com/Write-a-Fugue
Your friend Jean-Paul