Is it normal if I've had the nexplanon in for the first time to have a long first period?

Yes. As with most other "estrogen-free" hormonal contraceptive methods, cycle control is reduced with the nexplanon. This also goes for the depoprovera shot, progestin-only pills such as micronor (norethindrone) and ovrette. The fact is that it is impossible to predict whether a patient with Nexplanon will have amenorrhea (absence of periods) or prolonged spotting or even a full fledged menstrual flow lasting weeks.