Sad and frustrated

I've been pregnant 3 times is the last 13 months or so and have not been able to keep any of my pregnancies. I have a 10 year old and a 5 year old. It took 4 years of trying to have my 5 year old after my oldest. And now we've been trying for 2 years and all miscarriages. And I've never had them before. I have no idea what's going on. I do have more severe ovulation pain now than before.... not sure if that's a sign. And my periods are shorter.