Hello,
What is wrong with my baby?

Izzy has been sick for the past couple of days. On tuesday and wednesday he had runny stool, then on thursday i turned into bloody runny stool. He wasnt eating and when he did eat he would throw it up. so thursday i rushed him to the vet and he said that it could be colitis and that maybe he ate something or it could be stress. I cant think of anything that was stressing him out, we have been going about our normal daily routine. The vet gave him a shot and an antibiotic (Metoclopramide syrup). Ive been giving it to him since then. And the vet also prescribed this food that is supposed to help settle his stomach...it is in kibble form. He said by today it should start to clear up. But this morning about an hour ago...he got up and pooped in three spots, the last spot was runny with blood and it was mucus like (sorry to gross you out). Im wondering if I should take him back? Im going to call him when they open but I jsut wanted to get some other opinions. I have a feeling he has something else...I trust my vet but im not sure if he diagnosed him right. Its weird that he got sick because I took him about a month ago for his routine shots and he got the clean bill of health. What is going on?
I read about coccida and it said something about eating mice and other pests....now we did have a mouse in the house a few weeks ago...i caught it but im wondering if maybe he got a hold of the mouse droppings. Ive cleaned my floor many times since then but Im not sure. Please help! Im so worried!!