Why do you think she did this to me..... I am confused; Can GIRLS help me ?

So I met this girl in class at college. She was nice and seemed friendly.

She teamed up as my lab partner in Micro-biology, so we had to design experiments together. She would stare at me a lot and sometimes smile shyly. We didn't talk much except when we had to discuss the experiments.

We had some free time during our practicals and she started to talk and was a bit open by getting to know me.

After knowing her for 3-4 weeks at practicals, one day she abruptly was telling me how she didn't feel well (having cramps and nauseous).

She sort of awaited a response, so I told her to go and check with the doctor.

For that she replied, " I went with my boyfriend to the doctor".

She talked a bit on the experiment again and then we left.

I met her again a few days later and she had a smile when she saw me and i smiled back and kept on walking. ( I had class).

So I don't understand why she had to complain about her sickness and then mention her boyfriend....

Thanks:)