Still see a doctor and discuss it. It was likely not prescribed with the Nexplanon in mind.
What if a Dr prescribed it for me?
I would discuss this with your doctor. The reason being that even if someone were to reply here saying it's ok, it doesn't mean it's ok for you. Our bodies are all different, we all have different metabolisms, medical histories and related risks, etc. As far as I know, it's not ok to do this, but I would ask your doctor.
At the very least, you need to be taken off nexplanon and put on something else since this is causing constant bleeding for you.