Hi everyone, I created a throwaway account for this, but I could use a bit of perspective.

I had anal sex with a friend with benefits on the 30th of June this year, and received oral sex from her on the 7th of July. On the 29th of July she contacted me saying she thought she was pregnant, and I asked if she had a blood test, which is where it gets weird.
She said yes, she had had a blood test and the result was that she was not pregnant. I thought it may have been possible that my penis was inserted into her vagina on the 30th of June by accident, so it may be plausible.

Starting to think something is a bit off with her mentally, I said that I would take her to the same doctor on the 30th of July to confirm (I basically just wanted to see this negative result with my own eyes.)

The doctor said she was given a quantitative blood test a few days prior, and the results were negative. He assured me that there was no possible way she could be pregnant as she would have a higher HCG count than she had (I don't remember the exact number.)

Directly after the doctors appt, she still insisted on being pregnant, so I dropped her home and ceased contact with her, as I was beginning to think she had mental issues.

Fast forward to Wednesday the 8th of August, where I look at her Instagram and Facebook, where she is posting photos of her "baby bump", which I can't tell if it is her pushing her stomach out, telling her friends she is at 8 weeks pregnancy and having having twins, and that her due date is March 23rd 2019. I'm able to provide links to pictures in DMs if anyone can help me confirm whether this is just a girl pushing her stomach out, or a baby bump at 8 weeks due to twins.

I immediately make an appointment with the doctor she got the blood test with to see if anything had changed since the last time we spoke. The doctor obviously was careful not to give any information away about a patient while she was not there, all she said was "that the situation had not progressed since the last time we spoke." She also indicated she had not seen the girl since the time I took her there.

I really don't know what to believe, a google search for "False negative HCG test" indicates that sometimes the test can be wrong, which according to my doctor is such a small probability if the test was done that far into a "pregnancy". I don't want to contact her, as she's been seeming as if she's obsessive with me in the past, however I had no idea that her mental state was this bad if she's making the whole thing up. However, it's really been staying on my mind, and if anyone can offer some advice that'd be great.

Thanks in advance