Implantation bleeding???

My periods are very irregular. When I went to wipe on May 26th, what came up was very dark brown mucus. I figured ok that's odd, maybe I'm getting my period. I put a pad on but it never got stained. Next day wiping was very light and still brown. This lasted for about 3 days. 4th day was barely anything. I was using tampon just in case my period came down heavy but it never did. Tampon just had some light brown on it. On the 4th night I got bad stomach cramps and threw up twice. Last night nauseous and my breasts are slightly sore. Took a pregnancy test but said negative. Should I test again another time?