painful lump on my left calf

This isn't a muscle spasm that improves with stretching out, transient muscle herniation through the fascia that surrounds the muscle can occur. The muscle can then reduce through the fascial defect. Ultrasound can be useful in diagnosing these.

Sometimes a CT scan or MRI can help better determine what is going on. If it persists, you may need to see a surgeon for a biopsy.

If it is not visible, then most likely it's not inflammatory, because those are red, hot, swollen, itchy. Ganglion cysts (cysts located on the tendons) are by far the most common cause of otherwise not painful lumps unless touched. They are smooth surfaced, firm, mobile. They are benign and sometimes may disappear, although, at times may grown and cause even more pain due to compression.

The possiblities for this that I can think of instantly include an infection or a superficial venous thrombosis. I recommend that this be seen ASAP.

Did you get tested for Lime disease?

Go to your Dr. You must have this checked out.

to have evaluated. Can try warm compresses.

This must be examined to be diagnosed. See a doctor.

Likely a bakers cyst. A collection of joint fluid. Should go away by itself. Can be seen on sono

or a varicose vein. Doesn't sound serious in either case. But show it to your doctor just to make sure.