The menstrual cycle can vary significantly from woman to woman, but typically, it lasts between 21 to 35 days. If you had your period on 2nd Jan and then again on 23rd Jan, this means your cycle length is approximately 21 days. So, if you have a short menstrual cycle, it is normal to have twice menses in a month. Having a menstrual period twice in a month isn't necessarily abnormal, but it's not typically the norm either. It could happen for a number of reasons:

1. Short Menstrual Cycle: If your menstrual cycle is on the shorter end of the spectrum (around 21 to 24 days), you could technically have two periods in a single calendar month.

2. Irregular Menstrual Cycles: Some women have irregular menstrual cycles, which can result in periods happening closer together than usual. This irregularity can be due to a variety of factors, including stress, significant weight loss or gain, certain medications, or underlying health conditions like polycystic ovary syndrome (PCOS) or thyroid disorders.

3. Perimenopause: As women approach menopause, hormonal changes can cause menstrual periods to become irregular and sometimes occur closer together.

4. Bleeding Between Periods: Sometimes, women might mistake spotting or bleeding between periods (metrorrhagia) for a second period. This could be due to various reasons including hormonal imbalances, birth control, certain gynecological conditions, or in rare cases, it can be a sign of a more serious issue.

5. Birth Control Adjustment: Hormonal birth control methods can sometimes cause irregular bleeding, especially when first started or when switching types.

If you notice your periods are frequently occurring twice in a month, it's important to discuss this with a healthcare provider. They can help identify the potential cause and provide appropriate treatment if needed. As always, changes in your menstrual cycle are good to monitor as they can be indicators of your overall health.