Birth Control and Doctors

KJ
So, I have been reading through a lot of the other posts on this board trying to prepare myself for my potential life with my new birth control. I have read that a decent amount of people have the nexplanon or an IUD. Some are happy and some not so much, which is understandable, but to my question. 
For those who don't like it and waned to get it removed, but their doctors make them wait, is there a medical reason that they make you keep it? I know that there is a 6 month period of getting used to the nexplanon, so I was wondering if maybe they won't take it out before those 6 months because of that, or for some other reason?
I have the nexplanon implant, by the way, and I was just curious about it.