You may not be pregnant because you have a history of light periods. To avoid future stress you might want to try a different pill that will increase the flow a bit. These are the ones that I saw on a list for pills that are good for absent or too light a flow: Ortho-Cyclen, Ovcon 35, Brevicon, Modicon, Necon1/50, Norinyl 1/50, Ortho-Novum1/50, Necon 1/35, Norinyl 1/35, Ortho-Novum 1/35.