You can certainly try it, but if the zoloft is working, why would you want to stop it? Perhaps you can start some of the other things you mentioned, like exercise and/or diet changes, while still on the zoloft?
Also, depending on where you live, now might not be the best time to go off. I plan on tapering my dose this spring, once the weather is better and I can get out more. The sun has a big effect on depression, and you may want to wean off when you can get a lot of sunlight.
See what your therapist says, as she/he knows you better than anyone. But if the zoloft is working and you are not having negative side effects, then maybe staying on it for a while is not a bad idea.
Also, if the main reason you are on it is anxiety, the 9 month thing might not apply for you. My pdoc said that was for depression, and you risk another depressive episode if you go off too early..
Mom to two beautiful boys, now in school to be a therapist and help other women with PPD.