Implantation spotting after missed period?

I regularly get my period the 26th of every month except for this last month of april. So I missed my period and have been having some nausea and on and off cramps on my lower abdomen as if I would be if I was startin my period. It's been 5 days since my missed prd and in the morning I noticed 3 very small drops of blood only when I wiped followed with some strong cramps. I haven't bled since that time and took a pregnancy test later today around 6 pm and had a negative result? Could I have experienced implantation spotting AFTER a missed period if so how long after can I take a pregnancy test?