Sunday (the 31st) i had unprotected sex with fiance for the first time in a long time (he has been in on a business trip etc.). Monday (the 1st) i started my period (exactly on time) which was abnormally dark in color. Next day i noticed the texture was different. Wednesday (the 3rd) my period completely stopped?! Thursday and Friday was really light again, i just used lightdays rather than tampons. Saturday i didn’t bleed at all until late in afternoon only to stop completely all day Sunday. This whole time the blood was very dark and had a thicker texture almost tar looking as far as texture and almost poop looking in color just a little more blood looking. Now today i bled just a tiny bit (used 1 lightdays and filled it) but the blood was BRIGHT red/pink and watery!!

Are these signs of any sore of infection or could it be possible that i got pregnant on Sunday the 31st?

Additional Notes: My periods are very regular every 28 days and lasts for 5-7. The blood sometimes gets a little dark but not super dark, definitely what i would consider to be normal.
Also, i’m not on any birthcontrol or medication. I have been fighting a cold though…Could sickness affect menstration?