Private Issue with Cockapoo

Hi there, A few months my dog had a yeast infection and it cleared up with the medication. Now she has a big issue with her private area and it doesn’t look good at all. We went back to the vet a few weeks later and they said she hasn’t got a yeast infection anymore and that its just where she has rubbed her bottom on the floor and aggravated it. We got given anti inflammatories but it hasn’t got better. I feel like I’m spending loads of money at the vets for not the right solution and it’s just getting worse. Can someone help me with what this could be? She hasn’t been right since she was spaded. Thank you!