Help! Painful sex, swollen urethra, birth control, pregnancy?

Extreme details, I suppose. Proceed with caution. I am seventeen years old and on birth control, but I didn't realize until already engaging in intercourse that I have been on antibiotics that counteracted the oral contraceptives. I had finished my antibiotics and continued taking the pills. I am also... show more Extreme details, I suppose. Proceed with caution.

I am seventeen years old and on birth control, but I didn't realize until already engaging in intercourse that I have been on antibiotics that counteracted the oral contraceptives. I had finished my antibiotics and continued taking the pills. I am also taking prenatal vitamins for general good health and based on the rumor that they help your nails and hair grow. I discovered this may actually increase your chance of pregnancy by making your body more prepared for it. After engaging in intercourse, again, I noticed I felt extremely tight -- painfully so. He is extremely well endowed, and I am pretty petite. We took things slow, but I had to stop him. We tried again the next day, and I realized I was extremely sore and couldn’t even attempt it. I have noticed that I am slightly swollen on the inner part of my vagina, possible the urethra.

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Update: It's been a few days, with sporadic pain. We’ve engaged in sex numerous times, only rarely resulting in enduring post-act discomfort. I began to experience spotting of brown-blood, and I stopped my birth control pills. I’ve now begun to bleed with a very light period. My breasts have been sensitive and... show more It's been a few days, with sporadic pain. We’ve engaged in sex numerous times, only rarely resulting in enduring post-act discomfort. I began to experience spotting of brown-blood, and I stopped my birth control pills. I’ve now begun to bleed with a very light period. My breasts have been sensitive and the aforementioned boyfriend thinks they have “gotten bigger” or swollen. I’ve been resting and napping often, experienced moodiness, and even frequent urination. Also, when I attempted to consume alcohol the day before the swelling began to occur, it nauseated me. I (usually) have an uncanny ability to drink without a “chaser” and without making the slightest disgruntled face. Because none of the above-said things had occurred yet, I settled with mixed drinks. A few hours later, I vomited up everything in my stomach, drunk water and vomited that up as well. Although I’ve occasionally been nauseous, I haven’t thrown up since then.

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Update 2: I explained all of this above to a close friend of mine who has a toddler son of her own, and she is convinced I am pregnant.

My family is unaware that I’m sexually active at the moment, but it appears I have no choice but to visit a physician.

Anyone have knowledge or advice to share?
Update 3: EDIT: The "numerous times" I was referring to occurred in the past, not since this has begun. I have reframed from sexual interaction as of lately.
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