Is this menstruation or implantation bleeding? Had it for three days now kind off on and off and my blood isn’t usually this bright in color also I’m on Nexplanon (since Nov. 8th) maybe that’s why

UPDATE: So, I’ve been bleeding for nine days now. Well not bleeding but more like spotting, so for like two days after this post my “period” was pretty light and was like an actual period. But ever since then I’ve been spotting every single day and yes there is some brown discharge too, but there’s also FRESH blood. Last night when I though my “period” was over, after a whole 12 hrs at work I went to the restroom at home and when I wiped I was scared to see that I had started bleeding again and it was bright red. I hadn’t bled at all yesterday, so I was pretty upset. Then this morning, (I guess I hadn’t bled at night because I checked my pad) when I went to the restroom there was finally some NEW blood. It’s always a little bit but it still concerns me because I’ve never had spotting before and I’m also having some abdominal pain and can feel BUMPS too. I just can’t be pregnant, right? And doctors keep telling me that it could be constipation but they always try to avoid talking about my abnormal bleeding.