Is it possible for an 18 year old girls vaginal discharge to turn like a cream white? like it used to be only clear cum and now it's white too.

Yes.: Could be hormonal. Also, could be a vaginitis. Should see gyn to distinguish.

Can be normal: All women have some vaginal d/c that can appear clear, cloudy white and/or yellowish when dry on underwear. Many things can affect d/c. Abnormal d/c: accompanying itching, rash or soreness; increased d/c; burning on urination; cottage cheese d/c; grey or green d/c with foul odor. See your doctor if this is apparent.