Congratulations on your great report! In answer to your question, I think this is different for everyone and also it's important to consider all the factors involved--e.g., whether or not you worked during treatment, how well or not well your body tolerated treatment, what kind of chemo you had and for how long, what other kinds of treatment you had (radiation, surgeries, Herceptin infusions, physical therapy, etc.) and whether there were any complications with your treatment and/or long term side effects from chemo especially. My entire treatment from start to finish lasted for 15 months and I worked during most of that time. I would say I was fatigued for a year after I finished, but I had also developed other medical conditions not long after I finished treatment. Exercise certainly helped, but I learned to accept the fact that my body needed more rest after treatment than it had before treatment. Simply put, a little work, a little exercise, a little play--finding that new balance was what really helped. You will find your new normal.
Hugs & prayers,