I had a traumatic brain injury about 3 months ago and have experienced 1 menstrual cycle that was very light and none since. should i be worried?

Can happen..: A brain injury can upset your cycles. If this persists over another 3-4 months, you should see your gyn.

Difficult to tell: Without further information about the extent of your injury this is difficult to answer. It is possible that you sustained injury to the anterior skull base and the pituitary gland. I would discuss this with your doctor who may want to run some tests to evaluate this further.