OPK question! Help pleaaaasse!!

Kelsey • I have been trying to conceive my second child for two years... I am so happy that it has finally happend!
How many days can you get a positive opk
I've been testing everyday since the 10th and had a positive everyday.
Also I took one in the morning and one at night, the ones in the morning  are always darker then the ones in the evening.. Is there a reason for this ?