Its my 35th month on nexplanon and the past year i have been getting my period fairly regularly however it is now a week late. is this normal?

Probably normal: Menstrual cycles can be irregular with nexplanon. However if you are sexually active, it would not be a bad idea to take a pregnancy test because no birth control is 100% effective. If the test is negative and your periods continue to be irregular you can always see your obgyn for further evaluation to make sure nothing else is going on.