I don't think the downvotes are anything personal against you, your posts, and especially not your art. It seems there is a disagreement about rewards between some of the accounts giving you bigger upvotes and those that came after to disagree with the upvotes. I have seen it going on in a few other places and it usually doesn't have anything to do with the content creator but the people doing the upvoting. Try not to be discouraged and just keep on making your awesome content and fantastic artwork and i am sure it will all be fine in the end.