Hot nails

Duke was a little off after his most recent farrier appointment, so we missed out on several lessons.  I thought he was finally feeling better, and eager for a lesson, but John could see that he was short in the front at the walk, and confirmed he was off after one circle to the left at the trot.
John pulled out what I hope was the offending nail, and used a needle and syringe to put iodine in the hole.  Unfortunately, Duke felt the same the next day, so yesterday and today I have him on bute and have been soaking his foot in warm water and Epsom salts.
John said that a nail which touches the quick needs to be removed because it is hot, and then the iodine needs to go in to prevent infection.  I'm wondering if waiting a week let it develop a bit of an abscess (whereas if I had called the farrier the next day, he could have come out and pulled it out immediately) and that's what's bothering him now.
John said his feet were a little short (he's commented on that before) and also noticed his feet were cool when he was working on the nail.  Duke's feet seem to be sometimes cool and sometimes warm (although the warm might be just compared to the cool feet), and he seems to have his hind legs stocked up before he is ridden (but cool).
I'm kicking myself for thinking he was ok to ride - even though they were easy rides - after the two days off, and for not knowing to call the farrier and have the nail removed without John having to tell me.  My calendar has him off for two days, then a day off, then no comments for two days, then a comment he felt off again to the left.  I don't know if I didn't feel it those two days or if I ignored it.