you didn't mentioned what was your pap smear
Anyhow by using oral contraceptives the side effects you can have are,
which may be responsible for your discharge.
which you may thought as spotting.
Luekorrhea should be taken pathological only when it is more in quantity,
associated with bad smell and itching,
staining undergarments, need to wear pads.
If above symptoms are not there no need to worry.
But as you are telling that tenderness to touch is there and erythema
is there you better visit gynecologist along with pap smear report and get examined.