Why were you trying for a child when you just had recently one with someone else a year or months prior to the two of you dating?? You came into the relationship with a 4 year old and a 1 year old but were trying for a baby with a new person so soon??? Why??? Not trying to bash. Honestly curious.
Is this about your "lost" children? Replacing them???
Have you've made "peace" and healed emotionally and mentally with your miscarriages and abortions in therapy??
Also, sometimes when you stop trying, it happens.
For now, just focus on your other children.
Do the other children even want a sibling? Have the both of you set down with the children and asked them how they would feel about a new sibling?? Their input matters.
This could damage the relationship between you and all or some of the children.
This will change the family dynamics forever.
Would you still go through with it if they were adamant about not wanting a sibling??
If you go through with it, and they never bond and honestly hate the new sibling, how are you two going to handle it??
Since you two have a blended family and have been together 3 years... why haven't you married yet?? (If you haven't already)
Marriage isn't for everyone though.
Can you two afford another child?? Are your finances in order??
If it's meant to be, it will happen.
I would suggest you go to a fertility specialist . Maybe the problem is you, him, or none of you.
Maybe take this as a sign from a higher source that you aren't meant to have anymore children... possibly never, or just right now..
Whatever is meant to be will be.
You two have 3 beautiful children and each other to focus to in the meantime.
Enjoy life and what you currently have now..
If it's meant to be it will be.
Good luck