Wasn't pooping much...took to vet

Hey everyone! So my chinchilla Daisy hasn't been pooping as much and they have been smaller then usual. She has been acting fine but to be safe I took her to the vet today. They gave her a shot of Reglan and trimethoprim sulfa susp 0.50 cc twice a day. I also have been giving her gas drops which she loves (thank god)! I just wanted to ask everyone's opinion on the trimethoprim sulfa susp, I trust my vet but I wasn't sure what it was exactly and if I should give it to her. Thanks :)