Need advice... Clomid

Lacey • I am 26 and married to the love of my life.. We have 2 kiddos that will be 9 and 10 this year.. We are trying for #3...
Ok so I got started on clomid this past month, I am on cycle day 15 now so the doc said to bd days 12,14,16,18&20 so we are... When about should I start testing?? I've heard about some girls getting their pos before day 20.. Thanks ahead of time....