My legs are swelling after my runs

After both my Thursday and Saturday runs, I discovered that my legs were swelling, about 1 cm in the circumference around my legs and ankles. I first noticed this the evening after my run when I discovered my compression socks were fitting tighter than normal. I confirmed the swelling the next morning when I measured my legs at three points per leg. I reduced my run on Saturday to see if it would reduce the swelling, and it did. My socks were still tight last night, but not as much as Thursday evening.

I don't know if this swelling is normal after a heavy run, or if it is due to my blood clots. 1 cm increase in the circumference isn't a big amount of swelling.