A Haematologist is definately the way to go.
I had a huge DVT (ankle to belly button) when I was pregnant with my twins. The Haematlogist arranged genetic testing but he didn't find a genetic link even though our family history is a bit suss when it comes to blood clots. I was on clexane from 9weeks pregnant to 1 month after I had my girls.
Then suddenly when the girls were 5yrs old I went to the hospital with what I thought was Heart Palpitations and they found the PE and numerous clots in my lungs. I'm now on warfarin for life.