Possible pregnancy

Question

My periods have been late since August, before August I had a generally regular 29-31 days cycle. In august my cycle was 36 days then September it was 35 days now October I am on cycle day 39, hubby and I had unprotected sex this month on cycle days 12, 15, 17 & 28.  Im having cramps almost like period cramps but no period, my appetite has increased I used to go all day without eating until dinner and now if i do I'm starving, my nipples are tender on and off, and I also feel nauseous on and off, also sneezing or coughing I have a sudden cramp like sensation in my low stomach, took a urine test at the clinic mid afternoon yesterday (cycle day 38) and it was negative. The nurse recommended I go back in a week if I don't get my period.. My question is wouldn't it have shown up on a test yesterday if it was positive? Or is it possible its a false negative? My period has never been this late.