strawberries you are in the grip of extreme anxiety with obsessive thoughts and ruminating which is exhausting. Been there myself and my elder DD also suffers from it. You constantly seek reassurance but then there's always a 'yes, but what if...?' Being trapped in those constant painful thoughts and resulting panic severely impacts your ability to engage with the present moment. It's not something you can just stop doing, is it? I bet you would if you could.
So....I have found mindfulness meditation a help in the past but in conjunction with a low dose antidepressant and anti anxiety med. It might be worth considering. See your GP again and tell them your obsessive thoughts are very distressing and you need help and maybe therapy to deal with your anxiety. Don't be fobbed off. Consider asking for a referral to a psychiatrist because they are able to diagnose and refer you on to appropriate treatment. GPs tend to be jacks of all trades, but if offered meds it might be worth a go in order to see if they bring any relief. You deserve a life. You, and your partner. You can then talk again with perspective rather than panic about the possibility of having a child if that is what you both want. We can't predict the future. We only have NOW, and it's important to make now count, make it matter, make it meaningful.
Share your fears with your partner. Tell them you are struggling with anxiety and intrusive thoughts and you value their support and help in dealing with it. In doing that, you'll have reached out, with courage, and that in itself will be a good first step in facing your fears. Gradually, they will lose their sting if you take action.
You can do this. Take tiny steps, partner first, GP next, preferably WITH partner so you feel supported. ❤️