Four weeks ago i started feeling like vomiting but i let it go now my nipples are getting dark an i feel sick but i got a negative result an am bleedn?

Vomiting: I would recommend you get a pelvic ultrasound to make sure you're not having any pelvic condition and labs to check pregnancy and other hormonal levels such as prolactin. Do you get headaches? Double vision?

Morning sickness?: Have you had unprotected sexual intercourse or miss a menstrual cycle? If so, get a blood pregnancy test. I suggest a pelvic exam and ultrasound ASAP.