Has this ever happened to anyone?

can you ovulate with out it showing on a BBT chart i am using fertility friend and charting bbt without using OPK and for some reason this month it has not pinpointed ovulation my temps started low then just went up and stayed up i am on CD 23 i always have a 27day or 29 day cycle it said possible ovulation from cd15 til cd 20 but cant pinpoint it within a 24hr time frame Does it sound as if i have ovulated? Should i worry?