Question about pregnancy.....

So I had a healthy pregnancy with my son (1st pregnancy)..... and now it seems like I’m having miscarriage after miscarriage. I had a miscarriage In April and got pregnant right away just to have another one... my doc said to wait a cycle.. so I did.. tried again and now I’m on my period.. what if I’m not fertile anymore? I really want my son to be a brother and I want 3 kids :(