I have been using the digital ovulation test for the past couple of months and have always gotten a positive with them about the 11th day of my cycle....well my question is this: I usually test like 3 times a day when I start getting a lot of cm. Today I tested at 9 am got a negative, tested at 12pm and got a positive, but then I tested at 5 pm and it was negative! Can a LH surge only last that short period of time or is something wrong? This same thing happened last month as well. Please help!