How often do you get follow up exams or check up lab work? (I was diagnosed this year in January, so I'm still in treatment and followups are in the future for me.) Can I ask if there's anything specific that's making you worry about recurrence? If you're having specific changes, I would ask your doctor right away. You have a right to have your anxiety relieved. As far as taking Herceptin goes, if I have this right, Herceptin is an antibody that will work against a protein that some cancer tumors make. If you're not Her2+, then it wouldn't help.
I hope that you can write to the people on this board for sympathy and support, because we're all dealing with anxiety and talking about it to each other can help. Please do check with your doctor right away if you're having symptoms.
With best wishes for your health, Pat