Am I pregnant?

I’m on nexplanon my boyfriend came inside of me August 17th I was supposed to start my period 7 days ago. I’m getting cramps like a period and when me and my boyfriend had sex there was brown blood so I thought I started, I put a tampon in and took it out just now. There was no blood except this really sticky brown discharge on the tampon. My boobs were sore about a week ago but they’re not anymore.