I'm getting worried

I have been sexually active with my boyfriend for three years without condom use. I used to be on the shot and now I have had Skyla IUD for the last two years. I have never gotten pregnant even though we don't use condoms and I normally let him ejaculate inside me.

Right now my period is 3 days late and I had light spotting and cramps on new year's eve that never resulted in a period. I'm worried that the spotting/cramps was implantation. I've tried to make my period start but so far it hasn't. I can't afford to have a baby right now... I have a year and a half left of college and my boyfriend is leaving for basic training for the Navy in March then will be moving across the country for A School. I don't want to believe that I am because my BC is 99.97% effective and I know that isn't 100% but it's worked so far and I thought I was safe. Maybe not.. I'm not looking for advice or help or anything I just needed some where to talk about it because I don't want to worry my boyfriend yet if it's nothing. *sigh* I don't know. I just needed to vent. Y'all can ignore this if you want.