Ok, first of all, our body is made up of various different organs and systems serving different purposes, located in different places. Whatever you ingest or swallow, goes into your stomach and is part of your DIGESTIVE system. Hence, any semen or fluids or anything at all that's swallowed, will at best, be subject to stomach acids meant to digest it and will be used by the body and the wastes eliminated.
The digestive system is NOT connected to the reproductive system, so how can you get pregnant by swallowing semen? Let's assume that sperm somehow even survived the stomach acids when swallowed, but how will it go into YOUR UTERUS and cause a pregnancy? is the uterus connected to the stomach in any way?
I'd suggest reading up - a lot - on the human anatomy, our different systems, and most importantly, on sexual health, birth control, the female menstrual cycle etc. before you even think of getting sexually active since an unwanted pregnancy in your teens is the last thing you'd want. The other thing you definitely do not want are sexually transmitted diseases (STDs). Empower yourself with knowledge. Use the www and google wisely. All the best.