GF (21F) is acting suspicious about a pregnancy test, I’m (22M), together 1 year

Tldr: read the title

It all started when my girlfriend and I made out. We both had our underwear on, and we both were wearing jeans. We were just dry humping, and I did not ejaculate.

The next day, her period was supposed to start (I think—at this point I’m not even sure what’s accurate). But it didn’t come. As the days passed, her concern shifted from it just being delayed due to stress to the possibility of pregnancy, which feels very unlikely to me.

I was a bit suspicious at first, but I trusted her and didn’t push it. About a week later (today), I suggested we buy a pregnancy test. After some hesitation, we bought two. After buying them, she kept insisting that she would take the test at home and tell me the result later, instead of taking it while we were out, which I didn’t really understand.

Today, she took one into the washroom and came out looking very scared, even though she said the result was negative. That reaction confused me. I still chose to believe her and felt relieved.

However, she kept saying that the result might not be accurate and that she would take another test the next week, and possibly see a doctor to get things checked. She mentioned it could be something like a cyst, but I feel uncertain about what’s really going on.

While we were walking home, I asked if I could throw away the used test, she diverted the topic to the unused one, telling me to handle that. After some back and forth, she said she would take care of it herself and quickly put it in her bag, not letting me handle it. I didn’t understand why.

Overall, something feels off to me. She has also been acting differently over the past few days—for example, she hasn’t been comfortable letting me use her phone, which is unusual.

Could someone advise me on how to handle this situation and possibly encourage an honest conversation without damaging trust between us?