I had this with Implanon, though the bleeding wasn't heavy. I had terrible PMS and spotting all the time. My GP suggested the pill along with the Implanon, this made me anxious. The gp kept trying to get me to persist, in the end I liked and said I wanted another child so they took it out
It doesn't sound right to me - if you are concerned then it would be a good idea to seek a second opinion from a different GP.