Basically, I (25F) am really frustrated and I want to cry. But I physically can't because of my meds (Seroquel), so I'm panicking instead.

Background if you want. 
So, the old family dog has been with my stepdad (who I don't get along with) after the divorce with my mother, who I live with. I begged to take care of the dog as my own, yet my mother sent the dog away to practically spite my stepdad, as he didn't want him. Stepdad tried to sell him, but pretty much gave up and let his mother (who he lives with now) take care of the dog instead.
Recently my half-sister (16F) went over to the grandmother's house to visit. She took pics of him and showed me that the dog was obese- thanks to the grandmother's feeding proportions. He also has so much white fur on his face now that it shocked me. 
He didn't transition well to the new house. He always had separation anxiety. He also always had a tumor on his head, so maybe his fur is like that because of it...I don't know. In the beginning of the transition I got mad at stepdad for not wanting to get the flea meds/trim his nails, so I don't know if he's even been doing what he should. Or giving him the meds he needs to make the tumor painless. 
It's frustrating that the one that cares about him the most can't do a thing, because I live with my mother. I want to move out but I don't even have my bachelors yet or a 'real' career.

Please help with any advice...