No positive opk please help? X

Hi everyone

I've been doing opks for 3 months and not 1 surge. I have children with my husband, no problems before. I've got a bicornuate uterus but again no problems other than babies coming slightly early. Why would I just stop ovulating? I usually know by pains and egg whites when I am but lately nothing. Dr won't help as we have children

Thank you x

Ps I am using an own brand am and clear blue advanced pm and at 1 point it looked like it was getting darker but then lightened right up 😞