I have a second period week after my period, what does this mean ?

Count the days: You should count the days from the beginning of one period to the beginning of the next to give your cycle length. Normal cycle length is 21-35 days for adults. Cycles shorter or longer than this are abnormal. If you started 1 period on the 1st of the month, and the next on the 26th (=2 periods/month), that's normal, but if < 21 days, see your dr to figure out why.