Me And My Girlfriend (both 28 Years Old) Have Been

Me and my girlfriend (both 28 years old) have been trying to get pregnant. She has missed 2 periods and we have 10 different kinds of at home pregnancy tests that all say positive, however she has gone to the clinic 3 times now which say negative. What is going on? She has all the symptoms of pregnancy as well like naseua and sore breasts.