I'm confused about implantation bleeding

[tinky]

I started having the urge to urinate frequently when i wiped myself i saw light spot, it was dark brownish so i decided to put on a pad. For the whole week from light to brownish spot but then when i urinate it looks like heavy period. I felt bloated so i took urine test the next morning, the result was negative. Days passed my nipples get sensitive and i feel bloated like pregnant but my friends kept saying its because of stress. What's wrong with me??