nexplanon and pregnant?

I've been on nexplanon since I was 6 weeks pp. -itll be a year in april.- I've had periods that last for 3 weeks since the day after i got it put in, every month, on the dot. my period starts every month on the 11-13. well a couple weeks ago me and my fiance had sex, multiple times, then a few days ago I experienced what seemed to be implantation bleeding and I've had real milky and creamy cm. I've had stomach cramps and have been experiencing really bad fatigue and mood swings. I've been put on new medications here recently. could that counter act with the BC? could these be new bc side effects? I've heard that nexplanon can give false negative pregnancy tests, is this true? could I be pregnant? thanks in advance for any input.