There are many possible explanations for the small lump on your lower leg. However, to get a definite answer I recommend making an appointment with your primary care doctor
for a full history and physical. Some possible explanations include a simple bug bite (which would usually require only observation), an abscess
(which might require drainage and antibiotics, a lipoma (a benign fatty tumor), or a cyst (which can be observed or excised). Your doctor will ask about your past medical history, family history, any new medications, any history of trauma, etc and perform an examination. If your doctor is unclear what the cause of your lump is he or she might suggest taking a small biopsy
to determine the pathology of the lump. The results for this usually take about a week. Or sometimes the physician might elect to remove (excise) the entire lump, which is a simple procedure that can be done in the office with local anesthetic. It is very important to make an appointment with your primary care doctor to be evaluated as this is the only way to know for sure what the cause is of your lower leg lump and get appropriate treatment if needed.