Hi, sorry to hear it keeps getting infected.
Each time its got infected...ideally you should of had your shunt removed, been put on an EVD, put on antibiotics until the infection is completely clear, then had a new shunt put in place.
I was always told by my neurosurgeon, ''An infection, no matter how big or how small, is an infection, and all infections are treated the same.''
The fact that your infection keeps coming back, may be down to the infection having already spread, therefore once a bit has cleared up, a bit that hasnt has travelled down the tube to your neck wound again making it visible.
I may be completely wrong, but it seems possible.
Good luck and i hope this clears up soon, best wishes