When will you know when your next cycle come while on Depo?

Hi i'm 19 yrs old and I recently got my first depo shot September 23 the 1st day of my cycle. now I usual have a 4 day cycle but this time it lasted 7 days, I was also spotting a few days after that which I know is common. i'm just wondering when will I be back on my cycle or when will I be spotting again. also my boyfriend of 1 year and a month had unprotected sex for the 1st time ever a couple days after I was done spotting and there was a little blood basically spotting. Was that because of the Depo shot or was it because he was a little rough? FYI we both lost our virginity to each other back in June and we only had sex with each other. someone please help

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