I had a clot in my leg after surgery, and wow did that suckered hurt- for a long time too. I forget just what they called it now- but it was deep I guess.
It is called DVT, Deep Vein Thrombosis, and yes it was Extremely painful and I couldn’t walk for almost 2 weeks after getting the blood thinners. It took that long for the shot and pills to start doing their magic.