Your progression begins solidly enough in G minor. You move back and forth between the Gm (i), and a major chord version of the dominant D (V). Even though it's technically non-diatonic, this is quite common for a minor key song, even going way back into classical music tradition. But then you go to C (IV), which would normally be a Cm (iv) in the context. Because it's a major chord, it's going to disorient the listener a bit, and, if anything, the ear can hear it as a borrowing from the parallel major of G, or it will want to hear it function as a dominant and resolve to F, a fifth below. But instead it goes to E, which has no basis in either G, Gm or F. Since there is no movement by fourths or fifths here, only seconds and thirds, there is no real modulation occurring. I would suspect the ear is pretty lost at this point, only to be saved by the fact that you go back to the familiar Gm and D chords. I'm not around a piano to listen what it sounds like, but would be curious to hear what you've got so far. At any rate, you are in Gm, so you can write the rest of the song with that in mind.
Thanks for your input. I have been so busy since I first did this post, but I will try to respond to yours when I get the time. I have decided though that this song is definitely in D major, from the way I play it.
And there is also a G major in the song as well. I had mistakenly said there was not. Ok talk soon...
I'm often using chords I don't know the name of but then have to annotate when I write it all down. It used to be a pain but this site really helped me out. (And, actually, this particular feature was something I personally requested.)
This lets you enter notes on an onscreen 'guitar neck' and then tells you potential spellings.
The main Chorderator program lets you spell a chord and then get more or less all possible inversions displayed on the guitar neck. (You can set it up to use all sorts of different tunings, including completely custom tunings.) There's also the 'Scalerator' which displays all sorts of scales/modes on the neck.