Sick dog odd symptoms

About a week ago my dog started biting on his lower back so I gave him a bath. Later that day I found a spider in his crate. Two days later he started limping. The next day he started complaining when you picked him up. Today he started dragging his hind legs. And an hour ago he started vomitting and it's brown. I made him appt for Monday but is there anything I should do now with these new symptoms??? Please help if is four and a adopted pet and I am really concern.
   
Thank you.