I’ve had my Nexplanon in for almost 3 years, I only have 3 months left. I have not had a period...

It's amazing that you've not had any spotting or any kind of bleeding for that length of time. I'd suggest that it'd be a good thing to give yourself a break from artificial hormones, when you get the implant removed. Give your body time to reset itself, if you see what I mean.
It's certainly common to start spotting when you've been on the implant for a few years. The same can happen when people have been on the contraceptive injection for a couple of years. I think it's the body's way of telling us it needs a break, but that's just my personal opinion.