Hello,,, provided you have no other issues with your left leg or no trauma or injury , this pain may be due to strain on foot, due to walking on rough surface or irregular hard surface or excessive running or walking.
In that case good rest to your leg with some pain killers will help. Rest your legs to feel better. Ice helps. So can anti-inflammatory meds such as aspirin, ibuprofen, and naproxen, if you have no allergy or any contraindications, these are safe for you. You can buy them over the counter. You might want to see your doctor if the pain stays. Try not to do anything that makes your leg hurt more. Once it feels a little better, do some stretches. The next time out, wear comfortable, supportive shoes. And don't run on hard surfaces if possible.