Hi I've Been On Implanon For 26 Months Now And

Hi I've been on implanon for 26 months now and have not had any periods or spitting since the very start. This week I got my first period since having the implanon inserted and I really don't feel well as a result. I am fatigued, have really bad cramps, feel faint all the time and even feel nauseous at times, but it isn't very heavy. It's really taking a toll on me in work. Before having the implanon I never had problems with my period, even though they were quite heavy. I got the implanon purely as a contraceptive, not to control my periods, but it seems to be suddenly effecting me very badly. I was wondering if you could offer any insight into why this is suddenly happening and why the symptoms are so severe. Also, if I'm suddenly getting my period now should I be worried about the effectiveness of the contraception?