According to your excellent description, it may have been what we call Osgood–Schlatter disease
or syndrome (also known as epiphysitis of the tibial tubercle, or knobby knees) is an irritation of the patellar ligament
at the tibial tuberosity, meaning the ligament that goes from your upper leg and attaches just below the knee.It is characterized by painful lumps just below the knee and is most often seen in young adolescents; the typical scenario is that it starts giving more problems during activity or when playing sports; it is self limited, and many times there is residual ossification (hard lump) as a result of prior inflammation.
Dr Brenes-Salazar MD
Mayo Clinic MN