Help! Never had a positive OPK!

Hello ladies, I'm hoping someone can help reassure me that despite not having a positive opk in three months I've been testing I might still be ok for ttc? I have regular 30 day cycles, changes to cervix and CM as per a textbook and even get a small amount of cramping around the time glow says is my peak - but I've never had a positive opk despite religiously checking every day at the same time? Is it possible I ovulate really late? I thought a luteral phase was always 14 days?