Miscarriage after 3 kids

I am 39 yo be married twice, from my previous marriage I had 2 kids and one from my current marriage. All my kids are 9 years apart. After my 3rd child I start have miscarriage, as 2 miscarriages, I never had before, this feeling is the worse thing for me, since I cannot get over easy, the last miscarriage I had not my doctor but the on call doctor basically she told me isn’t any explanation because I had normal children before without problem, the only thing she’s said maybe because I am older now. I think isn’t enough answer for what’s going on. Please anyone can help me;? I really appreciate any advise! Thank you 🙏