Do you mean that you're feeling down after just getting a diagnosis? If so, I went through something similar when I was dx'd a few years ago. On the one hand, it was a relief to finally have an explanation for so many aspects of my life, but I did go through a bit of a depression, too.
For me, what helped the most was meeting other people with ASD (both on this site and in-person through an AS support group); that made me feel less alone. Hang in there.