Why is my period like this? Please read and answer... :(

Please, take the time to read it all... Thank you... Anyways.. I know it's normal for a girls period to change but mine never does and ever since I been TTC (only been for 2 months or so) when I get my periods they seem so off. They usually last me 5-6 days but it only lasted me 3 kind of 4 days this time. And I never really get cramps.. But when I first got it on September 11th (first day of period) I had the worst cramps and back pain I couldn't even stand up.. It was ridiculous.. But anyways my period only lasted 3 days. When I first got it, it wasn't even heavy and usually it always starts out heavy. It was medium I would say. I'm pretty sure I wasn't spotting because it was red.. And yesterday when I wiped, it was light red almost pink and I'm thinking seriously?? My period is done already? And then it changed to brown and that's what always happens when my period is done.. It was weird.. As long as I had my period for I never experienced this.. Does anybody think that there could be a chance that I am pregnant? I actually heard about a lot of woman before that got their period and we're still pregnant. I know about this one girl that had her period, it was normal and she ended up being pregnant and didn't realize it until the 4th month because she kept getting a normal period. Or they will mistaken it for implantation bleeding? I don't think I have that tho because I was actually bleeding like red at first.. Any advice?? Please and thanks