This probably isn't what your pup has but I wanted to letfolks know what happened with my daughters Yorkie. She noticed Ginger had some "bites" on her upper hip area that were looking swollen. When Ginger kept going at them we put an e collar on her. Well she used the edge of that to rub the spot and it was very bloody! So we washed the area put some cal-adryl ointment on it and was using a blow dryer to dry around the area before we were going to wrap it. All of a sudden blood sort of gushed up out of it. So Ginger got carted off to the 24hr Vets. Turned out she had a botfly larvae in it. That's right folks a maggot!!!
We of course were horrified but apparently it is not all that uncommon. The vet pulled it out and it was about as long as a pinkie finger nail and totally gross. Ginger is on an antibiotic for 10 days. These things are in the grass and will latch on when a possible host go by, or roll around on the grass. They then crawl until the find an opening either like a cut, bite or orifice!! Then they crawl in and set up shop. They need air to breathe so when we put the ointment on it it pushed up to get air and that is why the blood gushed out. No every time I see even a fly I want to whack it.