You could be. That happened to me I did think anything of it and a month later when my period never came I took a pregnancy test and went to the doctor and they confirmed it. The brown reddish color would be from the fertilized egg burrowing into you uterus. You could take a pregnancy test but I'm not sure if that is suppose to be done when you actually miss you period. I would still do it and then go to the doctor to make sure. They could do a blood test.
Thought I Got My Period. Started Late Wed. Night Dark Brown Then Tues. Red, Friday Very Little Just Enough For A Liner Then Sat,Sun Nothing @ Mon Spotted.Today Nothing. Could I Be Pregnant?
Usually light brown is the system cleaning itself out. As for sudden stops and starts in your period, this may be normal has it happens to most at some time or another. If you had unprotected sex, in the month before, this is always a possibility but I would not worry too much. Best you can do is a home pregnancy test. Best to do in the morning and use first urine as this is when it highest is hormones. Otherwise, everything should be okay, practice safe sex if you are trying to avoid, as well, worry can cause periods to be irregular