Why am I getting light brown discharge

Hi, 

I am 17 years old and since November 2017, I haven’t got my period. In December 2017  for a week I was getting this light brown discharge, which I thought was just my period, but there was no sign of red blood anywhere. And I know brown discharge could just be old blood, but surely if it was my period there would be abit of red blood. 

I do have the implant and normally my periods would be very regular and red! and I have had the implant  for nearly 3 Years now, so my body should be used to it. The other day I did get about 2-3 days of brown discharge.  I have done a pregnancy test and it came back negative. 

I’ve been tested for stds and I don’t any. Recently I have been bleeding a bit after sex with my boyfriend. I’ve been doing some research and it just keeps saying menopause!!! I know this is stupid because I’m only 17. I am very worried though. 

I just don’t know why I haven’t got my period and that I will go through stages where I will have this really light brown discharge. What could this be? 

Please someone answer and help me! 

Have you done any research in terms of possible side effects of the implant for brown discharge? I did a bit of research myself and I keep seeing that a lot of women get this issue. And they really don’t have any explanation besides this happens at some point after getting the implant.