I also find the SiS gels hard to open, either with teeth or by hand. Impossible with the two pairs of gloves I have to wear in the cold. Sweaty hands in summer also don't help. I find the Torq gels easier to open, with their slightly different design. But the easiest thing for me has been swapping to Shot Bloks, which are so much easier. I don't have to stop and walk to get them down either, so they're best for races.
I left my manky nail for ages. Finally went to the GP, and had to provide some clippings to be analysed to see exactly what prescription medication I needed. Three month course of one daily tablet, and it cleared up perfectly.