Hey there,
I am in the same boat, and have been twice before. The subchorionic haematoma is thought to be caused by a placental sheer, when a tiny part of the placenta sheers away from teh uterine wall. They vary in size and where they are located. They can heal themselves, and any blood wil be reabsorbed or bleed out causing no harm at all to the baby. Or unfortunately they can bleed out and cause miscarriage (though this is not as common) My last 2 haematomas were reasonably big compared to the one i have now, and my pregnancies were early but fine. This one is small (so i am told) and I have been bleeding with little and bigger clots for about 4 weeks straight now! hopefully all will be well. If you type in SUBCHORIONIC BLEED into google, you should find ALOT of info on them, there is a really good page made by a woman who wasn't so fortunate with her sotry but has posted up many other peoples. good luck to you and I hope all is well for you, as long as your haematoma doesn't get bigger all should be fine! fingers crossed! all the best! :)