What Causes Pregnancy Symptoms While Tubes Are Tied?

I have recently started having a few symptoms of pregnancy but i have had my tubes tied for about 5 years. My symptoms inclued lower back and hip pain, yellow fluid leaking from my breast, slight weight gain, a few head aches but not bad and now i have cloudly urine but all test are saying neg. I am now 26 years old, 92 pounds, 5'1" no major health issues three previous pregnancies no complication with any.