When to see a doctor

We have been trying for 2 years now. I had to have the first removed due it the baby not growing and making me sick and the second I had a tubal pregnancy and today I am having a miscarriage. That is 3!!! I don't know how much I can take it anymore. I want this so bad and my love does too, but when do you throw the towel in and go see someone about it? My obgyn said I am healthy and am able to carry but I can't seem to make it to term ever.