My Son Is One Yrs Old. I Am Not On

My son is one yrs old. I am not on bc. I keep up with my periods and I never be late or miss periods. I am 39days late with negative test but have few symptoms l was cramping for 3 weeks, slight headaches, dizzy, mood swings and food cravings. I don't feel the sick like I was with my son and also I got a positive pregnancy test on first try. My mother keeps saying negative test doesn't matter. What can be wrong if I am not stressed out? my last MP was july 31 2015 average 26 days which makes me 39 days late and 62days since last period