How do you know herceptin isn't working?

I am scheduled to start herceptin with taxol at the end of Oct after finishing 4 cycles of A/C. I am er-pr- her2+++ and concerned that herceptin may not work for me. (I'm in my negative mode right now). My onc doesn't do scans until there are symptoms nor does he do tumor markers. I'm stage 1 (grade3) and fearful of developing mets. I'm 46 premenopausal and bc was discovered by a routine mamogram. The doctors were surprized that they could not feel the lump, it probably was deep. Had lumpectomy with negative sentinal node for 2 masses 1.5cm and .4cm and am concerned that on path report it stated that there was possible lympathic invasion. My onc tells me right now I don't have bc in my body but I fear there is maybe 1 or several lost cells running around looking for a place to settle. I want to be very aggressive even overkill to destroy all of these cells. Sounds like for neg hormone people herceptin is the only drug and if that doesn't work then what?
Will my life ever return to normal, will I be able to make plans for the future? How do people cope with so much unknown?
Thanks for letting me vent