There are a number of reasons you may be experiencing light period flow. One very common one is that your hormones are fluctuating. Estrogen is the main hormone that affects your menstrual flow and if your estrogen level drops, your period will be lighter than normal. Even though you are only in your early 30s, this could be a sign you are entering perimenopause which can last for years before you actually reach menopause.
Or, birth control pills can also affect your hormones. The hormones in birth control pills can result in lighter periods and reduced menstrual flow. If this new trend of light periods continues, I would suggest speaking to your gynecologist to discover what is causing the change.