Hello. I Have Been Very Confused With A Situation. I

Hello. I have been very confused with a situation. I recently got my period but it was very different. I usually get my period the 25th -28th and this time i got it the 18th. I've been on birth control pills for 1 year and a half. When I got my period it only lasted for 3 days and I only experienced mild cramps for one day. But the blood was red the first day but not a lot. And the rest of the days it was brown and watery. I read online it might be implantation bleeding so i took a pregnancy test at home and it resulted in negative. I read online its common to get a negative result in between implantation, that results are more precise 3-4 days after implantation. Also, today and yesterday i have been experiencing vaginal buring and discomfort and during intercourse as well. And today i experienced white, thick discharge. Im very confused of what it could be because I have never experienced this. Hopefully I can have some answers.