What Causes Nausea, Pink Spotting And Bleeding?

my girlfriend last month started spotting for 2 weeks on and off it was light pink is a little darker then few weeks later after thought she started bleeding with a clot then this month she is been feeling for the past week or so nauseous before and after she eats in the middle of the night and early morning hours she has taken several pregnancy tests all came back negative what does this mean