Why is my puppy not eating or drinking?

Hello, I have a 5 month old maltese mix female. She has been eating 3 times a day and drinking water normally, but since yesterday she hasnt really been eating or drinking. Shes taking medication for bordetella and was doing better but now shes not eating.. shes still playful and goes outs on walks but there are moments where she just lays down and sleeps, whats wrong with her? please help..thanks she has most of her shots