First, schedule an doctor's appointment to get a blood test to validate the baby is yours.
Second, If your groin is itchy, proceed to unzip your zipper or pull down your shorts to scan for any crabs.
Third, if there are crabs, schedule another doctor's appointment to get prescription med to rid of your crab infestation.
Fourth, Check if you have herpes... Any area you suspect your girlfriend may have kiss or touched that area must be heavily examine.
You Sir, may have to seek counseling for your broken relationship as though it may be your only hope to save your relationship.
For the future, if you decide to bail on her, find somebody that will genuinely love you for you. There will be plenty of legal paper work if you decide to leave her and the baby.
It is best you seek advice from a physician for your S.T.D. infection.