What Causes Tenderness In The Left Calf?

2 weeks ago tomorrow, about 20 minutes into a 60 minute step class (that I take very regularly) heard and felt a loud snap in left calf moving from a lunge to jumping on to step. The elastic snap sound was immediately followed by a rebounding feeling in the muscle. Could not finish the class. Limped out. Iced it when I got home and rested. Limping got progressively better over the next 2 to 3 days to where I was not limping at all. No visible bruising, but tender to the touch, even now a little bit. No trouble flexing foot or going up on toes for over a week. Doctor really didn t give me much information other than to rest for a few weeks and then return to gym slowly.....much easier said than done. Cannot bear to not be in the gym but do not want to end up having to stay out longer than this last almost 2 weeks already. When is it safe to go back. Still feels a bit tight and hard, but not much pain. Don t want any Achilles trouble. I have flat feet and have never work orthotics, and have exercised strenuously pretty much my whole life. I am 46 YO now.