Good luck. I hope your pdoc can give you the answers that you want. The most common causes of volatile moods are bipolar disorder BP and borderline personality disorder BPD. Have a look at the definitions on the pysch central site- there is a lot of good info.
A major difference is that with BP the moods are caused by mixed up brain chemicals whereas in BPD it's more to do with how you think and respond to things... Meds and therapy are important for both but meds are more important for BP and therapy is more important for BPD. Just my thoughts on the two, others may have different opinions...