Giving up on a lot of kids

So, I always dreamed of having at least 4 kids. I grew up with 3 siblings who I am so close to and love dearly. I have always been the "mother" of my friends groups and my siblings. It was my absolute dream to be a mom and be surrounded by all of my kids. I have one amazing son who I am so grateful for. He is 3 and I desperately want to give him siblings. He is so good with other kids and so loving. We have been trying for another baby since August 2020 and have had 4 miscarriages. I don't know how much of this I can take. We had my son with no problems and my doctor can't figure out what is wrong. I hope I can at least have one sibling for my son and one more baby to love and cherish before this all gets to be too much. Its been really hard on us. I had to convince my husband to even keep trying after our last loss. So my plans for having a big family just aren't reachable. Our next baby that we hopefully get to have will most likely be our last. I just can't fathom going through this all again. It's just so hard to accept that this is going to be the end of that chapter of our lives. Don't get me wrong, I am so grateful for what I have. I have no idea what I would've done going through this without my son and my husband. I'm just struggling. We are talking about maybe trying to go into foster care down the line, but I'm not sure I am strong enough. Sorry for the long post. Just needed to get it off my chest.