Not all STIs have the same symptoms or cause the same diseases. Also, STIs often don't cause the same symptoms in different genders.
a. Neurological damage/extensive damage in other parts of the body, PID, sores/ulcerations, growths on the genitalia (this is different than sores) , eye infections (also one here commonly leads to major eye damage while others do not)
b. Some don't even cause infections in the genital tract (e.g. hepatitis, AIDS, diarrhea/dysentery) Remember that STI just means that it's contacted via sexual contact.
c. Genders: asymptomatic vs not; is painful urination a common symptom
d. Some diseases that aren't STIs can have symptoms that can be confused with STIs: UTIs, vaginosis.