The white stringy stuff you are seeing is most likely shed slime coat that built up while he was trying to protect the sores. What I would do is actually wait 3 weeks and then give him a final course of General Cure. That way, any eggs/larvae that were missed or were not susceptible to the meds will have grown up and can be eradicated. Depending on the type of internal parasite that he may have had, some stages in the parasite's life cycle do not respond to metronidazole and praziquantel, the main meds in General Cure.
During those 3 weeks, it wouldn't hurt to keep him on 1 tsp of epsom salts and any tannins/Indian Almond leaves.
It is very unlikely that any internal parasites are coming out of the sores. For him to have that severe of an infestation, he probably would already be a goner. :/