First, I'd recommend reading the other Q&A threads. This question seems to come up a lot and we tend to give the same advice.
Second, we'll need more information if we're going to be of any help. What kinds of things make you question being nonhuman? What characteristics keep coming back? Work from the inside out, not the outside in, in other words, don't have an end goal in mind. Just look at the evidence and go from there in your quest to narrow it down.