It looks like an infection in the skull/ brain, or internal bleeding but that should have stopped after a few days. I would say an infection is the most likely cause. As to treating, that is hard with amphibians because they don't tolerate many medications. Triple Sulpha (Tri sulfa) is normally safe but I don't know of many other medications that are. A vet that specialises in frogs might be the best option or call the local zoo and ask to speak with someone in the herpetology (frog & reptiles) department. See if they have any info on what can be safely used on them.