Advice for a Diabetic Yorkshire Terrier who started biting his toe nails?

About a week ago, my 8 year old Yorkshire terrier started biting two of his rear toe nails to the point where he nearly ripped them off. I immediately took him in to my vet who cauterized the skin & clipped the two nails as low as possible as well as put some "Quik Stop" on them. I was also sent home with a prescription of Clavamox and an e-collar to clear up any infection as well as stop him from doing any more damage. Things appeared to be getting better initially but over the course of the past few days I've noticed that he immediately starts to go for his back foot as soon as I take the e-collar off to try and give him a little "free-time" during the course of the day. One of the cuticles is also noticeably swollen, but does not appear to be tender to the touch if I massage his paw or put a little pressure on it. Does anyone have any advice and or personal experiences with something like this? To add to the compiling list of problems, he is also diabetic and gets 7 units of insulin twice daily, so is there a chance that this two things are related? I'm also aware that sometimes biting paws or constant licking might be an indicator of allergies but he only does it to one foot and the diet has been on for the last year is strictly prescription. BTW - I have an appointment to bring him back to the vet, but we can't get in until Friday (today is Tuesday), so I'm just trying to figure out what to do in the meantime. Thanks!!