Blood clots while pregnant?

I'm 7w4d and had a scare that sent us to the ER on Friday. I had terrible cramping and a gush of bright red blood. They did ultrasound and bloodwork and our twins were fine, strong heartbeats and all. 
I passed a clot the size of a silver dollar and immediately the cramping ceased and within an hour the bleeding stopped completely. Overall, it was probably only what you'd call "mild to moderate blood loss" meaning I filled up maybe half a pad in five hours. But boy it sure felt like a lot!! 
I'm already on Lovenox as a precaution even though I have no underlying conditions. 
Has anyone had any similar experiences with blood clots while pregnant? Did they go away? Was it a constant worry? 
Is there anything else I can do to mitigate the issue? Exercise?