My gf got an inplant n her arm to stop gettin pregnant but she says afyer we have sex the semen doesn't come bk out of her for days ! normal? good/bad

No and prob not true: She has the implanon, a small plastic rod impregnated with a hormone called Progesterone which prevents her from ovulating, thickens her cervical mucous and thins the lining of her uterus. It's an excellent form of birth control because it works 24/7 and is not subject to human error. Moreover, for many women, it leads to very light, or no, periods. Don't worry about the semen issue.