What Causes Abnormal Periods And Nausea With History Of Tubal Ligation?

I had tubal ligation in 2010 am now feeling nauseous and had weird period about 3-4 weeks ago with alit of mucus and brown streaked blood followed by mild period, since then I still get alot of mucus discharged and feel alot of movement and cramping on my lower abdomen. Am scared can you please tell me whats going on? I took 3 pregnancy test which theyvall had a very very thin line, am concerned that I might me further along just not know it. Am confused