I'm not real familiar with Herceptin and haven't had time to research it, so I'm not going to comment on the blood counts and leg pain.
I do, however, have a thought about the cold extremities. Do you have a port, and if so, are you getting blood thinners (either IV heparin or coumadin by mouth, or one of the other blood thinners) to keep it open? If so, that could well be what's making you feel cold.
Unfortunately, if that's the case, there's not much I know of you can do about it, other than bundling up. Increasing you iodine intake just a little (kelp tablets, maybe) and eating more thyroid healthy foods might help, but you really need to ask your doctor if that is ok, first. Also, ask the nurses if they know of any tricks to keep yourself warm. Sometimes support staff will know stuff the doctors don't.
Sincerely,
Tre