random question

I'm a little confused. so after I had my daughter I went on depo I stopped going March 15th 2017 I got normal periods right away. (7 days an medium bleeding)but the last 2 periods were really short an not what I'm used to. they were about 3 days long an only a very little blood basically spotting an then brown stuff I don't know what to do or think me an my boyfriend are currently ttc I'm trying to figure out when I ovulate if I'm ovulating at all! please help!