Calf Strain, wow talk about something that just seems to stay with you once you get them. I feel bad for you, because I know how frustrating these injuries can be.
I have tried everything with no success to keep this injury from coming back, until now.
Now certainly I cannot speak for you, however I will give you my assumption of what is going on.
First of all, a calf strain is nothing more than the muscle knotting up as you run, nearly identical to the muscle spasms you get sometimes in the back of your leg while you are resting in bed. Its hard to realize this because you are, I should say "Running".
Once the spasm knots up during your run, you will get a warning sign from the muscle to either stop, or slow down. Unfortunately as a diehard runner we all want to disregard the pain and continue to run through it. In most cases you will hear or feel a POP in the calf area, which means there is a slight tear.
Now to cure the problem, it will take a few days of running much slower than you usually do, and these stretch techniques, which have worked for me.
The two main stretches that should be your focus are regular bend over toe touches (touch the ground rather than your toes) and bend over toe touches with your toes on the end of something that will elevate them higher than the heels, probably 2 to 3 inches higher.
As you bend over to do these stretches hold steady for about a minute, then release and walk a few strides, then do it again. If you are doing this correct and not letting the knees bend, you will feel the stretch in your calf muscles. Do about 4 of these each way, regular with the toes level, and then with your toes propped up about 2 or 3 inches. After you finish your other stretching routine, you can now start your run at a very slow pace. As you are jogging get a feel of your calf pain and you may need to stop and stretch it again. But in time you will see by going slow and maintaining these stretch techniques things will be better.
As I said before you may have this calf pain for a while, or they may go away like mine did because of my stretching.
Good Day