A UTI can stop pigs eating, but as I understand it the wetness on the underside is usually consistent and other signs become obvious e.g. odour, crying out when peeing/pooping.
Is he still on Daktarin Oral Gel? I'd be inclined to stick with that for the full three week course, to clear any oral fungal problem (not necessarily recognised in a clinical examination). What dose are you giving, and how often? I'd also consider giving 0.2ml infant Calpol/chidren's Nurofen, as pain can also lead to the reluctance/refusal to eat.
I've got a 14 month old boar here (Elijah) who became very quiet, withdrawn and wouldn't eat; this happened only last week. Very unlike him. As he'd had the symptoms for only one day, just the one week of Daktarin Oral Gel cleared the problem up, but this is the time of year for fungal/oral fungal problems to surface. He did have a dose of Nurofen as well for the first couple of days, but I stuck with the Daktarin and it set him back on the right track.