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This lesion may be a hematoma from playing too hard and bruising this area. the best thing to do is to apply hot compresses to this area every 4 hrs. This will help draw any infection to the outside. Once it opens, flush it with peroxide and apply Neosporin to this area every 8 hrs. If your dog is still eating and active, she will not need antibiotics or the other medications. This will resolve with the treatment that I have described.
what do i do if it gets worse. i dont have the money for a vet right now is there anything i can do and thank you so much i will keep up with the hot compresses