late but not pregnant and I'm for sure

The fact that I took 3 prego test all negitave, late on pierod and still haven't started but also had a baby 5 and half months ago, don't know if it's normal to not have a pierod each time. I know I'm not prego cause I took test but I'm having hot flashes one boob hurts and head hurts and I feel bloated. Ugh when am I going to start