Nexplanon Implant

I had the implant put in in November 2014.

I had originally been getting 2 cycles a month, very heavy, cramps horrible, etc. I have an autoimmune disease that prevents my doctor from giving me the pill because it could leave me sterile at such a young age (19).

The first month i had a normal cycle with Nexplanon. My week had a normal blood amount, but since the end i have continued having spotting of very dark, think lining showing up everyday instead of any regular discharge. I was told random spotting would be normal for a few months, but does anyone else have any advice on whether this is normal and what to expect?