FenBen can cause a reaction to several nematode parasites.
Open wound like you describe seams rare. Red things is foreboding of red worms?
Cyst things could indicate Strongyle or other families.
I did 63 days of FenBen 5mg/kg/D. Other parasite phases now predominate. If you have a nematode infection, your posts provide little in terms of identification or corroboration.
The FenBen Challenge test does lead one to think nematodes. You need to learn more before using a single med. Most use formulas, or protocols. Dr Clark said it best when she said getting all the stages at one is the only way to succeed.
Blisters or Cysts could also be a symptom of the co-infection, meaning a complicated infection.
Stay on it, the more data you gather before heading off in a direction, the better off you are.