Bad results while on herceptin

[Jeanr]

I was diagnosed in august 2011 with breast cancer, the lump was mostly made up of pre-cancer however found traces of active cancer both within the dcis and lymph glands under the arm. I also tested positive for her2. I have responded very well to the first set of chemo (red devil) 3 month treatments. I then started on my weekly sessions, on the fourth session, i started my first of the three weekly herceptin treatment. Within a couple of days my lump had almost grown to the orginal size as to when i started. Now the oncologist says we should give it another three weeks of weekly dosages of herceptin to see how i respond. Has anyone expeirienced this before and does that mean that herceptin will not work for me?