Losing hope that I may be out this month...

Colleen
I am 6dpo after taking clomid this month. My temp was somewhat high until this morning when it dipped very low. I was told if I was pregnant it should stay up for upto 18 days. Is this true? My LH was high and positive the first 6 days but today they both decreased. I am already having mild cramps and am preparing myself to expect AF on 8/6/15