I had it happen to me once when I was 25. It is possible for your hormones to fluctuate for whatever untold reason, and just give you a totally random double cycle. Two for one sale on periods this month!
Typically your body ovulates once a cycle. Releasing one egg from one ovary. It is possible for an ovary to release two eggs in one month, or for each ovary to release one egg in the same month.
Two eggs in one month is one of the the ways that twins occur. There are two types of twins.
1.) Identical is when one egg splits into two during mitosis. Giving you two babies from one egg. These babies will look similar to each other, and be the same gender.
2.) Fraternal twins is when there are two eggs released in the same month and they both get fertilized. These twins can look different, and even be different genders.
Twins are rare, but they're not caused by anything being wrong. Having two periods in one month isn't the norm for most people, but it doesn't necessarily mean anything is wrong.