I have needed Plan B twice in the past 2 years. The most recent time was in August and I got my period within a week of the expected time and have been getting it on time since. The problem is my period is not as heavy as it used to be. It still lasts for about a week but a much lighter flow. Is this cause for concern? I took pregnancy tests back in September which were negative. Also I'm not on a birth control pill and I am a petite person if that makes a difference.