I Have A Sore Calf For Over A Week Now

I have a sore calf for over a week now , seems to be getting better these last couple days.. I'm thinking its a muscle strain.. no redness. no heat or fever , no swollen veins .. just a tiny tiny bit of swelling around the muscle but its hard to even notice you have to look hard . I work 6 days a week 10 hour days and I was wearing flat bottom shoes ( I know dumb) I went out and good new tennis shoes to help the problem. can I apply heat to the leg or will that make it worse . heat feels soothing