Thanks for all your help, ladies! More questions again tho - sorry!

As I said i would, I tested yesterday evening (7pm) with OPK and for the first time came up with a faint T line I know that still isn't really counted as a +ve result coz the T line is supposed to be darker than the C lines, but do you think that means I haven't O'd yet? Just seems very late (CD21 today). I'm going to test twice again today. We BD'd last night
My cycle is usually 30-31 days long. That would mean a very short LP, wouldn't it? I dunno, it's very confusing!!!!!!!!!