First of all take a deep breath and don't assume the worst. I too had the exact same thing. They sent me to the hospital for the ultrasound and didn't find a thing. So, it was determined it was muscle pain. Just as a precaution he put me on a two week regimen of aspirin. Frankly I've found the aspirin to really help with the everyday pains. Also the os wants me to take the aspirin when traveling - several days prior and post. Just as a precaution.
Now what they had me do to help with the calf pain was to lay flat on the bed witht he leg / knee flat, not on a pillow. Then witht he leg flat pull the toes as far towards your leg and then push the opposite. Frankly its just a heel toe exercise but you really have to work at it. It did take some time for that pain to go away for me. They've done several ultrasound "just to make sure" type of thing.
If it is something, and I'm not a doctor, you'll probably have an iv for 24 hours and then some medication. Don't expect the worst, but I know how hard that is. Let us know. Eagle