Depo

I had my first born august 18th 2004 after my six weeks was up i took the depo shot only once cause i was breastfeeding i bled for about 2 -3 weeks then it stopped and then i started having periods again but my peiod comes the end of the month to the next month so its like i`m having two periods in one month my daughter is now 1yr and 8 days and me and my husband want to try for a boy but it seems impossble and we have sex all the time . I don`t know to much about this depo thing but i would like to now what the hell is going on with my body.