Hi jessiekinnin welcome to HCM,
Penicillin interferes with the excretion of methotrexate
and thereby increasing the concentration of methotrexate in the blood and thus causing more serious side effects like lung, liver damage
, decrease in blood cell counts etc. So the blood levels of methotrexate should be monitored if penicillin is taken along with and should be adjusted accordingly.. But the interaction cannot produce swollen and painfull vagina..
It may occur as an allergic reaction
to penicillin per se and it is rare...
This condition is called vulvovaginitis which may be due to variety of other reasons like infections, inflammation, allergy
, swollen glands in the vagina etc. which needs to be evaluated..