What kinds of tests are available that can help diagnose why I have secondary amenorrhea?

Hormonal, anatomic. Secondary amenorrhea refers to absence of menstruation, after previous onset at normal age. Anatomic exam and scans (ultrasound or ct) can assess for obstructive processes. Hormonal testing can assess for thyroid dysfunction, pituitary dysfunction, excessive prolactin, and excessive androgens (either from ovary or adrenal) among others. These hormone problems interfere with regular menstruation.
Thanks for asking! A good history and exam by your gynecologist and some tests including blood test, ultrasound and laproscopic exam could help diagnose you secondary amenorrhea.