I have been trying to conceive for six months without success. for the past twelve months i have experienced light spotting exactly 7-10 days following my period. this month the irregular bleeding is much heavier. is this cause for concern?

Well: Well have you been taking medication to conceive? If yes you need to be concerned about the fluctuation of the hormones. Now if no then the body is most likely just adjusting itself. It is not abnormal to have an irregular period every so often. But see how you go if persists then time to see doctor for evaluation

Thyroid function.: Although 6 mo may seem like a lot, usually we like to wait 12 mo with regular "trying" before working things up; however, during this time it would be a good idea to do basic labwork, specifically thyroid function. You should go see your PCP and/or your regular ObGyn to establish care and state your concerns in order to start the proper workup early.