Welcome to healthcare magic!
Your problem is chronic, it is ironic that a trouble started by a virus taken over by bacteria and lastly has landed up in nonspecific inflammation.
YOU HAD ENOUGH IMAGING WORK-UP TU SUGGEST THAT THERE SHOULD BE NO INFECTION NOW.
But still I would advise you to have a CBC, CRP & Pro-Calcitonin
levels done, just to have an idea about nature of inflammation.
You had aggressive treatment with antibiotics and had initial response as well, I would advise at present to give time, may be the condition will resolve. You can undergo Mastoidectomy
later on safely.
Take tablet Lyser-D for 15 days twice a day after meals to suppress inflammation.
Get imaging about a month later only if you have symptoms.
I hope this advise would be helpful for you.
Wish you a great health!