By seeing your complaints it appers that you are suffering from erythema nodosum
whch is very common on shins, it is due to many causes including infection like streptecoccus, histoplasma, catscratch disease
and many, some drugs like oral contraceptive pills
may also cause this, before you take specific treatement punch biopsy of leisin is advisable which is confirmatory secondly x ray leg to rule out sarcoidosis and TB, throat swab culture to rule out streptococcal infection
, then continue NSAID'S, if does not subside steroide may be needed, oral pottasium iodide is very helpful to reduce inflamaton, and most important treatment of underlying condition, stop OCP and adopt other methods of contraception
. dont worry this condition is not dangerous but leads to very disconfort, consult your doctor and suggest my opinions also to him.