Ummm what is going on with me?

I am not sure what is going on with my body. I have been on the implant for four years now, the first implant i had, went brilliantly, it stopped all form of my period as well as my really horrible cramps that i was having, but when it came to having it replaced, my period had come back and my cramps are more horrible than ever. I don't mind having the period again, it is just that they last for 3 weeks then it will go away for a week and come back again for another 3 weeks, i have spoke to my dr about it and they have said that it will only last a little while till your body gets used to the new implant but it has been over 6 months now and it is still happening, i haven't been able to make an appointment at the Dr's yet as they don't seem to have any available appointments. But i was hoping someone will be able say what they think is going on with me....... please help me