can an 18 year old get cancer, and if not .. advice??

i've always been extremely healthy and haven't had any big medical problems. i ususally ignore symptoms but lately, i haven't been able to do so. for the past few months i've had severe abdominal pressure and bloating, it's highly uncomfortable and i can't find a good position without feeling pain, i've had extreme gas and nausea and i have thrown up like twice a week for the past month, i have constipation, and i can eat about a sandwhich a day, but no more, i get full really quick (NOT like me), i've had really bad back pain, i've had light periods the past 3 months (this is like unheard of for me-not pregnant)i can't feel awake, and i had to go up a pant size because my stomach was so big. i never go on the internet but i looked up these symptoms and ALL of them go under ovarian cancer. i hate the doctor so i wanted to get an opinion before i made an appointment. can an 18 year old get ovarian cancer? what else could these symptoms be?? thank you in advance!!