Dyan, I think the situation is that the immune system has finite resources. That is, it can only destroy so much at a time. It seems as though for many ITPers getting certain strains of the Flu can sometimes lower counts and sometimes rise them with other strains.
Since the Flu is a virus, antibiotics does not have a direct beneficial effect. When ones immune system effectively eliminates the virus, based on previous reports here, things/counts/treatments should go back to normal.
You mentioned having single digits in January. When counts do drop soon, perhaps you should do the same thing as you did then. Take prednisone for a few days?
If you don't mind me asking. You mentioned having migraines with high counts. When your count does suddenly drop soon, do you expect to get a migraine when that happens too?