Getting frustrated!!

Holli

nornally i use clinical guard ovulation tests but i ran out so i grabbed some first response ones. the past 2 mornings I have gotten 2 lines on my tests but they aren't quite equally dark yet BUT when I test in the evenings ...it's no line at all.....why???? when I test with clinical guard I got my peak in the evenings and I feel like I am missing my peak.