Sexy everyday or every other? Help!

Cassie
So my fertile window is from 4th feb - 9th feb. I have a 27/28 day cycle which leaves me with ovulating either day 13/14 ( I always get a positive opk on the cycle day 13 at night ) 
I have read doing it every other day is best:
I'm confusing when to do it now?
1: Should I start on the 4th and go every other day?
2. Start on 4th and go every other day plus the day of opk positive? 
3 start on 4th go every other day plus cycle day 13 
4. Start on 4th go every other day plus cycle day 14 
Soo confused! 6 months trying - can't get it right!!!