Usually when a person has a yellow/greenish discharge it is an STD...possibly gonorrhea or clamydia, but curable with antibiotics. If you have multiple partners you can never be too sure if they are STD free because everyone don't get symptoms. To be on the safer side always use condoms and if he refuses then simply say no. Its always better to be safe than sorry. At 14 years old you shouldn't be having sex and none the less with multiple partners you dont want to get labeled by other individuals. Just be careful you don't want to contract an STD you can't get rid of...also tell your parent that you want the HPV shot to help prevent you from getting cervical cancer which is an STD/STI ( sexually transmitted disease/ sexually transmitted infection). Good luck sweetie!
The best advice i could give you is to get it checked out by the doctor and have a vaginal swob done to rule out any infections, best to get it checked out quickly and don't be shy doctors have seen it all, good luck.