Here's a few things you should know about bipolar

- Average bipolars cycle 4 times per year
- Bipolars can cycle daily, but that's called ultradian cycling; it's very rare
- Severe manics can have mixed states where they experience symptoms of both disorders
- The average age of onset for bipolar symptoms is 17 years old
- Psychotic features (i.e. delusions) only occur in very severe cases

Here are a few more things that make differentiating depression and bipolar difficult:
- SSRIs like sertraline (Zoloft) are well known to occasionally induce mania in certain, genetically predisposed patients. This iatrogenic mania does not count towards a diagnosis of true bipolar disorder. (They're separate)
- Many depressed patients coming out of a depression feel manic when they're actually just normal. They're just regaining their normal functioning, and it feels a bit over the top.

I'm not sure this will clear much up for you, but it should make you a little bit more informed. I'd consult a psychiatrist. It's possible your Zoloft induces mania, and s/he may want to add a mood stabilizer.