From weekly to 3 weekly treatments?

My oncologist wants me to switch from weekly to 3 weekly treatments of herceptin as there seems to be no sign of any mets after herceptin/navelbine combination last year. I'm understandably a little anxious about this as I feel certain my weekly shot is what has kept BC(round 2) at bay for the last 18 months. What is everyone else doing and what is working for them? I'm concerned I'm being asked to switch because it's more convenient for everyone (me included!) and that I haven't been given any medically proven reason why the switch should be made.