A month ago I sprained my ankle playing basketball and didn't think anything of it, but the next day my calf muscle was really sore as well. After a week it didn't seem to be getting any better, and after I noticed chest pain when taking deep breaths a quick trip to the ER confirmed there was clotting in the vain and several of the clots had travelled up to my lungs.

After several sprained ankles and pulled muscles in the past, it took me for a loop that this injury could be so different. At first it just felt like a pulled muscle, but after getting on blood thinners the pain localized near the top of my calf, almost at the back of the knee (where the remaining clots were collecting). It took three weeks before I could even flex the muscle without significant pain. The clots are finally breaking up though, and it's feeling a lot better now.
If it's been three weeks then it probably is just a bad tear, but you should make a trip to a pt or sports medicine doc just to be safe. The one who sent me to the ER said that sometimes people can hobble around on a fractured fibula/tibia (can't remember which one) without even knowing it, and if it's taking longer to heal then there could be some tendon/ligament damage. Anways, a visit could definitely speed up the healing proces (they can show you the best exercies to do to make sure you don't work the muscle too hard).