Hi.. My Partner And I Had Sex Last April 5,

hi.. my partner and I had sex last April 5, i had my period on the 13th and we did the deed again that same day but my menstruation stopped on April 14 (Note: only 2days and bloodflow was really light just used 2 pads for the whole 2 days) I took nordette as precaution on the 16th and observed the EPC dosage - 4tabs then 4 tabs again after 12 hrs). Took home PT test April 22 AM and it was negative. Now, April 23, I'm experiencing spotting (very dark brown and there are clumps of blood). Is this a side effect of Nordette or could i be pregnant? Help please...