nexplanon and no period

So ive had the nexplanon implant for about a year now. When i first got it i would bleed for about a month. As time went on i started to spot more or have a lighter flow but still get something every month. Last time i had sex was on Feb 14.I was  spotting   very little during this time. I continued to spot for about two weeks but it was very very light. I didnt get my period for march. On march 15, a month after the last time i had sex, i took a test and it came negative.  Since then, i have tested 3 more times and they are all negative. Should i be worried about a possible pregnancy?