Need help!

Okay ladies got a question. I have been on the depo shot for over two years. got my last shot January of this year. I was supposed to go back in March but found out I was able to have another baby. Since the end of March I have been bleeding. Well stopped and thought I might have been pregnant but took tests and blood both negative. Still have spotting bleed like I was having my period then stopped but now having spotting and this time it heavy spotting. How am I going to know when I'm actually on my period. Any advice would be greatly appreciated. Thank you in advance.