Had what i thought was anormal period,then a week later bled again for 4 days.i had unprotected sex 3 times before this.could it be implantation blood?

Unlikely: Implantation bleeding isn't as common as many people think and, when it does occur, it's within 10 days of conception. I hope you understand the consequences of unprotected sex. If you're in a committed relationship & both of you want a child, that's wonderful. If not, you're playing Russian Roulette with your life. Just think about it, please!