implantation bleeding??

(Had a baby 13 weeks ago) Have had 2 period so far. First one was 16 days long, started my second when I was suppose to and it only last 8 days. I had unprotected sex on the 16th of January. Started my period the 20th. Is there any way I could of gotten pregnant then and that this is implantation bleeding now? My period ended completely on the 27th and I have had no more bleeding since then till now. Today has been 15 days since I have had sex. Please respond!!