Hi,
Well usually the brown discharge comes right before or after a period, usually not 2 weeks after although it's not that uncommon. Has your periods been changing in any other ways? I just turned 38 and have been noticing some changes and am concerned about pre-menopause so I'm scheduling a doctor appointment to see it that could be happening already. You mentioned you are 43 so I just wondered if there are any changes you may be having and if they are related to menopause. I would keep an eye on it and see if it keeps happening, then if it does schedule an appointment with your doctor to discuss what's going on. Could be just your body cleaning out the old blood, but a little late :) Good luck to you.
Brown spottting during mid-cycle usually indicate fertile period where an egg has just been release from your ovary. But with your age I cannot say. Sometimes old blood that has not been shed properly during menstruation do spots during mid cycle.