Greetings, sorry about your pain. I will address your concerns in two aspects
A. If you have varicose veins you will have pain as ypu described. rule this out first. If positive go with advice of physician.
B. If the problem you described is as you said in your description, then not to worry. It is just a muscle spasm (trigger point)
Next Steps
get a very good massage to calf, lower limb, all over the body by a physio or any ayurveda masseur. you should be about 50% better in first session. do get couple of session to relax your muscles.
Health Tips
not a medical problem to be worried. after your massage sessions do let me know how you are doing.,will update on exercises and stretching to make sure it never reoccurs. reach me at time to clarify your doubts