Ovulation tests

Heather • Mother to one boy, three babies with wings, pregnant for the fifth time
Has anyone used ovulation tests? I'm trying them this month and I'm using the test strips you use every day for 20 days or until you see an LH surge. Glow says I'm two days into my fertile period, but so far I've only seen a very, very faint test line. Shouldn't I be seeing the line gradually get darker?