Slight pinching...on right side

I am scared I am supposed to get my period tomorrow it will be my second period after my ectopic. And I have these little cramps here and there and I want to make sure I am fine. I had sex on the 5th I am supposed to get my period today has not come yet.  I took a pregnancy test this morning it was negative.  Now just a few seconds I had a pinching or stabbing in my right side could that be implantation is that why my period is late?