I'm a 18 year old on the nexplanon for birth control , I had sex 3 times on two different days (03/11/17&03/12/17) after my last period (03/10/17) . Start date was on the 28th of February. We did use condoms but my boyfriend did cm inside of me . I ovulated on 3/17/17, and on 5dpo (3/22/17)I had light brown spotting just a few drops, which Im sure was implantation bleeding. I missed my period on (3/31/17) , I didn't ovulated on (4/14/17) which was weird to me , so currently I'm 24 days late as of today (4/24/17), next expected period is on (4/28/17) . When I have my periods I spot a day or exactly on expected period . Today (4/24/17) when I wiped I only saw pink light spotting. Nothing on pad or underwear, I tested on 4/18/17 for urine and blood test came back negative . I've had all symptoms of pregnancy but test show otherwise, what can be going on ?