Weird mid cycle spotting?

I got really sick at the beginning of the year and ended up missing 2 pills (not back to back, about 3 days apart). I was also on 875mg of Amoxicillin (antibiotics) for a sinus infection. I started spotting on the 19th of January, by the 20th I thought I had started my period 2 weeks early as it was red/pinky but extremely light. Needed a panty liner but could have gone all day with just one. By the 21st it was back to spotting, and for the 22nd too. By the 23rd it had turned to basically black sludge looking spotting and now on the 24th I just used the bathroom and it's light red mixed with brown only when I wipe. What is going on? An early period, a chemical pregnancy, implantation bleeding, a withdrawal bleed from missing the pills almost 3 weeks ago?