period is late ..... what to do??

Cassidee
Ok so my period is now 10 days late.  I started bleeding the 17th kinda like a period but wasn't as heavy and my regular period was supposed to start Jan 11-15. Could this be implantation bleeding? 
Also I tested a few days ago on Jan 17th and it was negative the same day I started bleeding. Should I be worried that I could be pregnant?