Nexplanon Question

So I've been on the nexplanon now since of October 2017. I had my regular period like last week. Was normal. Actually started eariler then what I was supposed too. Well yesterday I started spotting again and this morning I'm cramping really bad. I mean clenching stomach bad. I know it's common to have irregular periods and bleeding on this but this is the first time this has happened to me. I took a pregnancy test it was negative just as a little breather. Really so confused and these cramps are no joke so bad I want to go see my doctor. I have had kidney stone surgery last year but idk if that would effect it because I haven't had any problems with it since. No symptoms of a uti like nothing. You guys have any thoughts? Or is the nexplanon just being evil with me for bleeding this month.