First period after baby

I had my second child, a beautiful baby girl on December 28, 2016. I have yet to have a period and she will be 4 months next week. My period came at a decent time after my first was born in 2013. My husband and I had had sex three times, using a condom all three times, and had gotten a deppo shot in the beginning of March. We waited two weeks before finally having sex without a condom. I had gotten a pregnancy test when I got the shot and it was negative and will be getting another one in a few days when I go back to the doctors.

I was just wondering if this has happened to anyone else after having kids. I'm 28 and have always had a regular period until now. No cramping, spotting, sore boob's, or any other sign of my period coming.