Why is my BBT flat after ovulation???

Melissa • I`m a newlywed who just got married August 23, 2014. My hubby and I have officially been together for 4 years and are trying for our rainbow baby. We lost our first at 8 weeks in December. <3
I ovulated CD16/17 and since my temps are flat at 97.7. Fertility friend said they now can't predict my ovulation. Anyone know why this is? Temps are supposed to rise after ovulation.