Your body can digest cum (from now on called vaginal fluids for a female and ejaculatory fluids for a male) just fine and if you are a female performing oral sex on a male, you will not become pregnant by swallowing ejaculatory fluids.
THE BIGGEST AND MOST IMPORTANT CONCERN WITH ORAL SEX AND SWALLOWING EITHER VAGINAL FLUIDS OR EJACULATORY FLUIDS IS SEXUALLY TRANSMITTED DISEASES (STDs). If a person has an STD, they are very likely to transmit it to your mouth. This is an effective route of transmission for many STDs, such as Herpes 1 and 2, Human Papillomavirus (HPV), Gonorrhea, and Chlamydia. Many times people who have STDs do not even know it; thereby, increasing your risk of getting an STD.
Do not rush into anything - Oral sex like any sexual activity needs to be discussed between you and your partner before the situation arises. Also, it is a good idea for you and your partner to see a doctor or go to a teen health center. A teen health center can see you confidentially (you do not need your parent's permission) and on a low cost or no cost basis. The teen health center staff can give you and your partner information on safer sex guidelines, STDs and birth control methods. If you live in Northern New Jersey, please call the Adolescent/Young Adult Center for Health at (973) 971.5199. If you live outside of Northern New Jersey, please look up your local Planned Parenthood.