Real symptoms?? I need input!

Nickey
My last BCP pack ended on January 31, I started my last "pill period" on February 2 and ended around the 6/7th.  Me and my boyfriend BD'd a few times during what could've been my "fertile days" which was between the 13-18th.  AF isn't due until the 28/29th.  I don't chart my temps or take ovulation tests so I am unsure of true dates.  Recently, I've been having nausea, headaches, excessive burping (which I NEVER burp), and sore breast (but not to the touch, just achy).  
This morning I woke up and have some cramping and lower back aches but AF isn't due for another week. 
Could this be implantation bleeding? Has anyone had these symptoms so soon and were actually pregnant?