Positive and then negative pregnancy tests.

Hello ! My friend had a second line on her pregnancy test last week on Sunday but then afterwards she kept getting negatives. She’s been having symptoms one week before her period is due. Her period is due tomorrow. She’s still cramping, feeling the nausea and everything else.

I wonder if she’s having twins? Has anybody here gone through something like that ever before ?

Thanks in advance. This is a really confusing situation and we would like a clarification.

Any advice?