Four Periods, three negative pregnancy tests, and a lot of worry.

My girlfriend and I had intercourse approximately 4 months ago, on August 4th. Although we'd had sex before, this was the first time in about 7 months due to a long-distance period we were going through. We weren't careless, and used a condom like usual, yet at one point, whenever I pulled her on top of me, the condom broke. It was one of many spermicidal condoms that she'd had for about 2 months throughout the summer, anticipating my return to be a bit earlier. I must've been a bit off not to realize the state of the condom, which was a bit more adhesive and tighter than normal, as if it had melted to my skin a bit, and didn't move at all.

By the time it snapped, neither of us had finished, especially myself due to the restrictions of the condom. I promptly pulled out and after talking about what happened for a few minutes, we continued for just a little while, using one of the other kind of condom's we'd had at the time. For the record, we haven't had sex since this occasion.After about two and a half weeks, she felt a bit sick, so she took an early pregnancy test. This was taken in the morning, and turned up negative. On the 22th, 18 days later, she received her period, but was missing the 4th day, of her usual 5-day cycle.The next month, her period came on September 13th, roughly 9 days prior to when it should have came. This one was normal in duration, the only thing different about it being the time of the month.Her third period was perfectly fine, happening like clockwork on October 13th, with her last and fourth period being received one day later on November 14th, which isn't too unusual, as we'd never really tracked her period before this all happened, and one day doesn't seem like much.Although she never really experienced any early pregnancy signs, as of late, she's been experiencing nausea, stomach cramps, and has been feeling hungrier as of lately. After about a week of this happening pretty consistently, we decided to have her take two more pregnancy tests. At this point, it would've been 4 months in, and due to the HCG levels at this time, the chances of a false negative are slim. She took one in the morning, and one after her typical 3 and a half hour afternoon nap, which she's been taking for roughly a year now. Both were clear negatives.I'm 18 years old, and she's 16 years old. Both of us work, well-- I'm between jobs right now, and I'll be starting work again in approximately two weeks, and we'd already come to the conclusion that if she was ever pregnant, at our current age, that she'd want to get an abortion. Due to her age, and the need for parental consent, it's a bit difficult trying to get her in to see a doctor to know for sure. Her parents aren't aware of us having intercourse, despite 3 years of dating, and of course, she'll end up seeing one if the symptoms persist, but I just felt I'd reach out instead of shouldering the problem myself.Although the chances are extremely low, I worry a bit about the timing as well, because I wouldn't want too much time to pass, in the chance that she is pregnant, and end up being pigeonholed to a full pregnancy against our wishes.As far as weight goes, since the time of what would be conception, she hasn't gained any weight, instead losing 4 pounds. (Going from 126lbs to 122lbs) Because of my new job, the winter season, and just simply the want to enjoy life, I've really been wanting to put this all behind me, but it seems to be impossible due to my sense of paranoia. My girlfriend and I are very open with each other, and she rarely expresses any concern over the matter, unless I panic, which typically scares her due to myself being the calmer of us, by far. I'm fairly certain that she hasn't been tricking her body into thinking that she's pregnant, as she rarely ever thinks about it, and doesn't view it as a strong possibility.On the other hand, when I talk to people about the problem, or she talks to her parents, the first thing they mention when the symptoms come up is pregnancy, which adds to the constant reminder of what could be.If anybody could shed any light on these matters, it would be greatly appreciated. Thank you for reading.