Hi Eponine,
I think your frogs injury is definitely infected. I will tell you what I would do... Get a bottle of sterile 0.9 normal saline in the first aide section of any store near the pharmacy area. Get a jug of distilled water from the bottled water area. Only use distilled water for this mix, not for regular soaks. Mix the 0.9 normal saline solution with the distilled water into a 50/50 solution. Very gently drizzle it daily over the wound daily, then apply original Neosporin (NO pain reliever...just the original...the pain reliever type is toxic to them) to the area with a new Qtip each day.
Call a vet...the best treatment would be either and/or both Metronidizole and Baytril systemic drops and topical silversulfadiazene cream to the area daily. These are prescribed medications which are dosed by a vet per your frogs size. Dr. Frye will often prescribe them for your frog after an email. Keep in mind that tomorrow is Friday and they will be closed for the weekend. I'm not sure of your budget, but if you could have them shipped over-night shipping, it would be best. You will not need the neosporin if you have these treatments. You need to act quickly though.
Dr. D. Frye, DVM
(734) 439-2273
Email:
dr.frye.vetatmilan@gmail.com
Website:
Milan Area Animal Hospital, about Milan vet clinic, M.A.A.H.