What does this mean?

my girlfriends period was 20 days late and she made an appt with her doctor for next week and she took 3 pregnancy tests and they were all negative but she had symptoms of pregnancy (we just had a miscarriage 2 months ago) and her period came but she didnt have cramps or anything it was really watered down like it was red kool aid and it was spotty then it would come down then stop and spot again what could this be?