like Lilly Ivy said shes probably tired and nauseous from worrying if she is pregnant.
If she is pregnant, there are 2 options if you both feel your too young for a baby.
1-abortion,
2-adoption. you could give the child to a family who wants a child
and you two would not have to raise this baby.
You and your girlfriend have to be honest about this with her mother, she should know, because then she could get your gf on Birth control, and help you both come up with a sollution.