Answers please

I missed my depo shot appointment and I haven’t my period for a couple of months. Usually when I don’t make it to my appointment on time my period usually comes, but for the past two days i been spotting but my period would’ve came already. I don’t feel the symptoms of it coming but it’s not a lot either like how it usually is. But the spotting is a mixture of red & brown. I took a pregnancy test two weeks ago but came out negative . I need some answers please !