I gave birth to my thrid child on 30th of oct. 2010 and 2mth later l fixed nexplanon 68mg implant since then I ve not seen my period, but I breast fee?

Probably normal. Most implanted contraceptives, including nexplanon, implanon, and Mirena (levonorgestrel) iuds will cause cessation of menses while they are actively dispersing hormones. This is typical, and should not worry you. They are also safe with breastfeeding your child.