Any advice thanks

I had 2 depo shots in 2014. I had my first af on 2nd Jan 2016 next one was 39 cycle then I had a 32 cycle my next af started on 2nd April had for 4 days. I got up this morning & when I wiped there was brown coloured discharge as the day has gone on it has got lighter in colour & is nearly back to normal. We bd on Wednesday the day after my af finished any ideas why this has happened thank you