Based on what you've told me, you have a 6-month-old female maltipoo who is sick with a cough (although it's getting better on Clavamox) but is also now not eating, vomiting, and having diarrhea.
That means one of two things is going on to make her not eat...
1. The Clavamox is upsetting her stomach and causing her to lose her appetite, or...
2. She has some type of illness that is causing the vomiting, diarrhea, and appetite loss.
Either way this warrants at the very least a phone call to your vet, if not a visit. Your vet may want to try switching her to a different antibiotic, or may want to see her to try to determine what the cause of her appetite loss is.
No matter what, you can rest assured of this: once she's healthy her appetite will return.
So, the answer to your question of what do you need to do to get your dog to eat is, get her healthy.
I do hope that helps to answer your question.