I know this one's probably one you've considered, but your toothbrush...
Are you replacing it after each infection or are you sterilizing it? Also, do you keep yours in a cup with others from the household? If your son or husband is a carrier you could possibly be reinfected each time that way. I know my daughter loves using mine or DH's toothbrush from time to time, sometimes just to chew on (she calls it brushing her teeth)...
My in-laws got us an UV toothbrush steriliser a while back as DH is always bringing nasties home from work. This has seemed to have helped cut down on illness in the house since we started using it.
Hopefully this last lot of antibiotics will do the trick for you Sevans!