little help from the experts

ca
Ok ladies I need one more time your help. 
I got my period on  05/07/2017  last only 3 days    And is every 28 days my ovulation predictor showed the I was ovulating on the 17-18  we did BD all my fertile days according to this app my period starts on 3 days from today and other apps say 7 days from today. 
 5 days ago I started with sore Naples and this morning got a very very small spot after I wiped     Old blood brownish. Pregnancy test comes negative. 
Thank you baby dust for all.