I haven't had my period for 4 months already is this normal?

Amenorrhea. If your cycle has been regular previously (28-34 day intervals) and you have tested negative for pregnancy (serum HCG test is very accurate), this is not "normal". Conditions such as severe stress, PCOS (polycystic ovarian syndrome) can produce long intervals w/o "periods". See your gyn provider for testing and recommendations.