Pulled calf muscle?

[Twilkes]

I was using the calf press machine at the gym, you lean against an almost vertical chair with straight legs, and then almost stand on tiptoes to raise the weight up (may not be a calf press machine). I overdid it a little, lifting too much weight, and felt a tiny burn in one leg so stopped immediately. Didn't feel injured at all, just that I probably would have been if I'd carried on.

Thought nothing of it for a few days until I realised that I was still getting a tight feeling in my calf, patricularly after periods of non-activity (ie sleeping, sitting at a desk). It feels like it's a muscle maybe 2 inches in diameter, on the inside/rear of my calf, about a quarter of the way down from my knee.

This must have been about three months ago now, and it doesn't seem to be getting any better. I cycle to work and it doesn't bother me at all during any kind of activity, only when the muscle is cold and hasn't been used for a while.

Am I destined to have this forever, or is there something I can do to help it recover? I had a sprained ankle that I still noticed 18 months later, is this just another slow recovery injury?