Sorry to hear about Max. I hope he is doing better.
If he were my dog, I would take his temp & if that was normal I would then not feed him for a meal or two & see if it improves. If he had a temp or if the symptoms lasted more than one day then I would get him to the vet.
Of course, you have a wild card with the melanoma, so in view of that I would at least call my vet ASAP.
Good Luck & Keep us Posted on How Max is Doing,
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