Itchy And Sore Vagina

I ahve been sexually active a couple times. but i have noticed that lately i ahve been having alot of discharge and it smells bad, like sour almost. and i notice it from just sitting in a chair. itr almost feels like im sweating all the time. but i dont usually sweat. and just a couple days ago i noticed it was very itchy and i got out my little picket mirror to take a looka nd there was a red sore. buteveryone (3) that i ahve been sexually active seem trust worthy enough that they didnt give me any STDs or STIs but there is a questionable guy who i didnt have sex with, but we made contact. So is it possible he gave it to me?? i know he ahs been with alot of girls and he is alot older. and he is now having a child. so it makes me think he is clean. because if he gave the mother any infections they would know through the baby, or they would want to be sure before having a baby. OR is it possible to have a yeast infection at my age of 17? or should i be more concerned? i checked the symptoms of a yeast infection and i matched all of them. but it doesnt make sense to me, because they said is was for older woman at a child bearing age or they had diebetes. but im neither. so whast going on???