Ttc for 6 years without using anything

So me and my boyfriend has ttc for 6byears without using any kind of products or anything to help us out i have 3 kids by another guy and I have went to the doctors to get tested to make sure it wasn't me n my bf has a baby in heaven that never made it to earth so my question is with this ovulation how does it work if you have irregular periods because mine has never been regular i have ovulation tests (clear blue brand) that a friend gave me but I need to know how to test and if anyone can help me understand this whole ovulation that would be great thanks