Miri,
My advice for you would be to seek advice from your doctor. Sickness, and tenderness in the breast can sometimes be an indicator of pregnancy, but I would test again.
In fact, I would go to the doctor for a test, rather than buying your own home kit considering you have already recieved mixed results.
As for the discharge and diarrhea, mention this to your doctor as it may be a key part of his diagnosis.
All the best
Are you sure the first test you got was positive? It's not common to have a positive and then 3 negative right after. I would go get a blood test done to confirm whether you are or not. Many things, not just pregnancy can cause the symptoms you describe.
^Helpful tips here, a blood test is more relevant then going for a urine test, even though u should do it in the morning, because your hormones are strong enough. Plus, I got the same brown reaction, but this was the end of my period. Sometimes I do get a liquid smooth and sticky reaction.
wait out another few days or weeks, then go for the blood test, the results will tell u honestly if you are positiver/negative.