To support what Justkeep said, I know it's hard but the fact that they found no problem can be a good thing. I had 2 miscarriages and I was so sure there was a problem with me... and here I am, at 36 weeks. We did nothing different, except that it took me a bit longer to get pregnant this time.
I don't know what your situation is exactly, but I read somewhere that recurrent miscarriages could be that a woman is "superfertile", and that unviable embryos can implant too easily. It reassured me thinking maybe that's what happened to me, although I'll probably never know. (With both miscarriages I got pregnant right away, without even really trying)
Maybe it was just bad luck.
The fact that you already have kids is only a good sign.. don't lose hope.
I hope your therapy will help. *hugs*