The answer to your question depends on the length of your normal cycle. If your cycle is shorter than average, say 24 days, it is possible that you would have two periods in one month and you should expect another period in 24 days. However, if you normally have a 30-day cycle, then something has probably interrupted your usual cycle. Sometimes this happens and there is no explanation. Other times it could signal a problem. Would you consider your bleeding atypical for your period? Have you been experiencing any cramping or unusual pain? Do you have any vaginal discharge that does not seem normal for you? Are you sexually active? If your answer is yes to any of these questions, you should follow up with your healthcare provider to discuss other possible reasons for the irregular bleeding.
Since I don't know the exact dates, I would suggest that you go back and count the days between periods. Remember, your cycle is your own and can change. You may have simply had a shortened cycle one month. But you should try keeping a calendar and checking out what is a normal cycle for you. My sisters and I had our own calendars when we were in high school and we put a dot (or a period - get it?) on the first day of our period and then ran a line through the days for as long as the period lasted. That way we could visually see how long and how often we were on our periods. So, don't try to count more than one for a "month," but rather keep track of the cycle period.
I've had the same thing happen to me before. Every so often, I'll have two periods separated by only 2 to 2½ weeks. When the second one starts I usually sit there for a quick second thinking to myself, "I thought I just had this." I usually count my second one for the next month. Then my period goes back to behaving itself, coming once a month. Though some girls have an unwavering time period of 28 days between their periods, there are girls like us who don't have that same luxury. However, if it's happening more than once in a great while, I would talk to a healthcare professional.