Ovulation question

Hi.  I have been tracking my ovulation using an at-home kit, but the test line never quite looks as dark as the control line.  I know my LH level is changing as I go from no test line to a line, but anyone else have this happen, where the test line never seems quite dark enough to call it positive?  Also, once you get a positive and keep testing, should it stay positive for awhile or go back down right away?  Thanks!