Ask the doctor to give you an ultrasound or x-ray to check for pieces of placenta that didn't come out after the last birth or if you need a scraping of the uterus that is what happened to me and since then I have been better. The lining should come off and shed in patches not all in one Clump not sure if that is normal. Your uterus should do small contractions throughout the whole period not just one large one not sure what that's about. Could it be several miscarriages in a row?
Passing clots like that isn't usually normal- I don't think it would have anything to do with the surrogacy, but I'd recommend giving the doctor a call and going in for a check up to see what might be happening since it started all the sudden and is happening regularly.