Positive OPK

I am just wondering why is it that you shouldn’t take a opk with FMU? I took one a few weeks ago and believe I had a positive but I had a chemical last month and I am supposed to be on AF but haven’t gotten it nor any symptoms. I took a opk this morning just for fun and got this.... could I be ovulating twice in one month after a chemical or am I extremely late for ovulation after my CP?? Any one with advice or similar situation?