45 year old woman; last menstrual period 1 year ago. today, noticed brown discharge that used to indicate period starting. should i be concerned?

Women-perimenopause!: You are most likely still in peri-menopause. This can be a several month issue, or nearly a year long issue. Irrespective, you are young for menopause. Younger females entering menopause are at increased risk for cardiovascular disease if not given hrt (estrogens). You need tests for fsh and estradiol. Women need to consider the fact of early osteoporosis. If not on hrt, you need something!