I have not had my period in about 6 months, and I am not pregnant. Should I be worrying?

I don't think you should worry per se, but you should be concerned.

Missing periods happen for a variety of reasons, such as big shifts in weight (especially weight loss), strenuous exercise, stress and hormones craziness.

Six months is a long time for any woman of childbearing age to not have a period (aka amenorrhea). You should see a doctor, discuss your dietary and exercise habits and be evaluated for hormonal abnormalities. Your doctor may have some recommendations for bringing your period out of hiding. You should also get a pelvic exam if you haven't already had one lately. A pelvic exam can help detect any physical problems with your reproductive organs.

In the meantime, read M.I.A or, Dude, Where's My Period? for more info about missing periods.