First post scared! Whats going on? Am i pregnant? Help!!

Im 12 days late and have done 3 pregnacy tests all negative! I had the tinyist bit of spotting when I was two days late with cramps but no sign of my period at all since! I thought that this may be Implantation? But surly if I was I would have got a positive result by now? We have had unprotected sex and I have had other symptoms feeling sick on and off, tired and frequent urination but scared its all in my mind! What do you all think??