More positive opks than usual

I am going on 4 days straight of positive opks .... and this isn't the first time this has happened to me... one time just to see I took opk and it was positive yet I got my period 3 days later?.... this cycle I checked my cm and cervical position and it all seems to match but I'm still so confused..... could this be an infertility problem... or just that its taking my body longer and when or what positive opk do I go by to start intercourse? Please help I'm very confused?