3 miscarriages in one year

Jj • Mother of 2 👨‍👩‍👧‍👧 due with my 🌈 June 2019

I’ve had three miscarriages in one year. The first one was around 8 to 10 weeks in the second one was at 15 weeks where I had a collapse of my uterine wall I believe. The third miscarriage was at eight weeks. Has anyone else had this happen and what was the cause? I’ve had test ran on all three babies but came back with absolutely nothing.