Ttc for 6 months

So I’m a mother to daughter already but her biological father don’t have nothing to do with her due to being a drug user and he physically abused me throughout the whole relationship.

Anyway I’ve found someone else and got engaged 4 months ago we are trying for a baby for about 6 months now. My periods are so irregular and also I’ve been getting a period every two weeks which cannot be normal so I made a doctors appointment which they done blood tests and they also done a examination which they took swabs all come back normal. Is anyone having this or had this.

I’m gonna get a second opinion next month but I buy opk to try and find out when I’m fertile and I get close and then I test the next day thinking it going to be positive but I never have had one so I’m gonna start testing using opk more than once a day when I nearly get my positive one. Can anybody offer anymore advice.

Thanks