Could Cramping In Abdomen And Spotting Be Due To Implantation Bleeding?

I had my last period from 1 to 4 February, was sexually active on CD 10, 13, 14, 15 and 17. I started experiencing cramping and stretching feeling in lower abdomen from 21 Feb and then light bleeding (bright red blood) from 23 to 24 February. I feel tired and weak all the time and am have nausea without vomiting, and stomach still dull cramp in abdomen. I took HPT on 23 Feb and 3 March but they are negative. Could I have had implantation bleeding?