Nexplanon- help!

I got Nexplanon right before I started this semester at college (early/mid August) and am worried something is wrong. My periods have been abnormal since, which they warned me about. First I had spotting then my period was 12 days. I didn't have another period for a couple weeks and now I've been on my period for 17 days and there's no sign of it slowing up. I've gained weight and have acne too. Should I go see a doctor? Could something else be wrong?