My dog may be sick... help?

[Agg Doll]

My dog, a female American Staffordshire Terrier, I'd say maybe 5 years old, started acting very strangely. She looks like she's done something wrong, her ears back and tail tucked but no one is yelling at her or anything to make her think she's in trouble. She wants nothing to do with her food or water. She is usually a very high energy dog and affectionate. But, since about 6 hours ago she's just been moping, and hiding. And when we fed her I think she took one bite and started gagging, like a human would who had the stomache flue I guess. I was petting her and noticed this growth on her back as well... I thought it was a tick until I noticed that there was a few strands of fur growing out of it. The tip of it was black and the rest faded into her skin color. I just noticed this growth today, and I have no idea if it has anything to do with her mood.