Symptoms continued after light periods

Maria

I had my last AF on 11/12/2016. My symptoms started after 27 December when I suddenly started having heartburn and nausea with a weird bloating. The next week bloating got worst with more nausea and heartburn specially after meals, I started to have unexplained pain in my hands and ankles at night and occasional headaches. Had a hpt (internet cheapie) at 8/01/2017 which was a bfn.

I got what I assumed af at 9/01/2017, a very light unusual flow first two days and then brown spotting once or twice a day for day 3, 4, 5 and 6. I still have cramps and nausea after meals. The bloating got severe and have backache. On 13/01/2017 I had a beta HCG blood test which was < 1.2 (a negative). Another bfn on hpt at 15/01/2017.

My question is is that any way that I am still pregnant and couldn't show in the test for some reason? How many days after implantation bleeding stops that we should test? mine stopped at 14/01/2017. Also I had the bleeding on one day before my expected AF.