Am I pregnant? What should I do next?

[Jmv25]

No pregnancy symptoms earlier, but have been very stressed about the possibility of it. I haven't been sleeping which has caused fatigue and sometimes feel sick to my stomach when I am thinking about it but that's obviously stress. Had gotten some sore pectorals and ribs from the stress (but my breasts weren't sore). On the pill, which I have taken every day on time. I got my period 7/21. I got strep and finished my penicillin 7/29. I had intercourse 7/31 with just the pill for protection. I just took my inactive pills for this month and on the third day got brown discharge and the last two days have been just barely spots of red/pink. It's been extremely light which is unusual. I feel like it isn't even a period. I took a pregnancy test at home during the 4th day of my non active pill (2nd day of the "flow) and it was negative. Could I be pregnant or what is happening? I've never had a period that was so light (if I can even call it that).