Dear ncassis: Initial testing at the time of diagnosis is often done to get a baseline and make certain that there is no metastasis. The exact testing may vary according to physician. It is not common to do routine scans after primary treatment for breast cancer. In general, the follow up would include blood work, a mammogram of the remaining breast, and a physical examination. Scans would be ordered if there were any symptoms or if there is a reason to order one. If you are concerned, you could get a second opinion but you may find that most physicians approach breast cancer follow up in a similar manner.
Unless you are very dissatisfied with your Oncologist for other reasons I wouldn't advise a change. Her opinion is a very popular one among the Medical Community. Survival is NOT lengthened by finding something by scans over discovery when symptoms appear. PET scans show many false positives.