Your opinion is greatly appreciated!

[b]I came across this site so I thought I’d see what you guys think. Is it possible to be pregnant if you had sex twice (pullout method) while on antibiotics and BC around the time of ovulation and then at the time you’re due for your period you bleed enough to wear a liner for three days and it’s a dark brownish color but you got a negative hpt the day before you start bleed and still neg a week later (3 days after bleed)? About a week and a half before this "period" was feeling (and still do feel) bloated, lower backache, minor cramping, very hungry, very thirsty, emotional, tender breasts, minor headaches, more prefquent urination. Or could I just be experiencing something completely different?

More detailed info:I had my regular period Dec 17then was put on amoxicillin for 10 days (which decreases my BC) then on Christmas and Boxing day had sex with my husband twice but he pulled out. (this is the week Im fertile, 3 days before ovulation) and then I got my "period" on Jan 14th but it was light, lasted 3 days, only had to wear panty liner etc as I described. I took a test Jan 13 (before I bled) was neg. Then on Jan 18th I took a test (3 days after I bled) and was still neg. I know some people don’t show pos. until maybe 6 or so weeks but some people experiences early preg. bleeding so Im wondering if that’s what this "period" was, or if it just happened to be lighter??