I had an ultrasound because i'm experiencing abdominal pain on the left side. i was told that my lining is 8mm. is this something to be concerned about. i haven't had a period since sept 2013. and i've had no bleeding since then. just consistent lower

Concerned yes.: The measured thickness of your uterine lining is at the top range of what would be considered normal for a "post-menopausal" woman. Several options are available: a trial of progesterone, endometrial biopsy, D & C or simple surveillance. Discuss these options with your health care provider. BTW: this finding might be unrelated to your abdominal pain. Best wishes!