You could have missed your first positive as you weren’t testing 2 time day you gotta test at least 2 times a day between 11am and 8pm. Cd 18 looks close. Ewcm doesn’t mean ovulation it means sperm can swim in it. If you want more accuracy you need to add BBT to confirm ovulation. Opks don’t confirm ovulation or dpo. If you add bbt you will know when you ovulated, dpo, luteal phase length (is from the day after ovulation to period which stays the same each cycle give or take 1-2 days. Average length is 12-14 days give or take 1-2 days.) when period is coming by temp drop or if you miss your period and your temp stays up then there is a chance for pregnancy.