it's like this down the side of my right foot
Looks like mine, which only occurs now on the outside edge of my left foot near the base of the little toe. It does sometimes spread to the gap between the little toe and the next one. Canesten sorts mine out.
A course of Lamisil was no match for my foot and nail fungus, which again laughed it off. Hideous side effects too - beware.
very rarely psychiatric disturbance
If none of that works, try asking for Lamisil at your GP. It's a tablet version, but he'll probably be loath to give it you if it's not severe.