One of the possibilities for such kind of knots
is erythema nodosum. It results in reddish, painful, tender lumps most commonly located in the front of the legs below the knees.
Diagnosis is by physical examination and biopsy of the lesion.Other lab investigations like complete blood count, ESR,ASO titer, urinalysis, throat culture, intradermal tuberculin test, and chest x-ray may also be done.
I would recommend a physician/dermatologist’s evaluation.