Last Af july 23rd!

My last period was july 23rd aftwe being late for 3 weeks took a few pregnanxy test and all bfn then it finally show up july 23rd, im now on cycle day 65 and still no sign of af took 2 pregnancy test about 2 weeks ago and bfn i really don't feel like buying anymore pregnancy test since last time i wasted over $80 and and then af showed, my concern is that im about to start the law enforcement academy and they make me do alot of physical workouts, what are the chances of being pregnant even though i have no symptoms and bfn...if not pregnant what could be causing me to be so late