When to start opk? Here’s my story.

So ladies my 2 most recent periods were August 18th & September 12th. I’m not sure how long my cycles are but I do know my periods last 7 days... I didn’t do opks last month but I’m trying to do them now but only problem is that my period is suppose to come next week but I have been having brown discharge since Monday 10/2 with a neg preg test today.

Would I wait until next week to start? It still do opks & count the brown discharge as cycle day 1 even if it was a week before period is due?