I have sex about twice a week and always use condoms and I am on birth control that I usually take it on time with the exception of a few days a month I take it an hour or two late. I had my period on time, but it was very light and only lasted about 4 days. I'm scared that it is "implantation bleeding" or something like that. I heard of women having their periods for the first little while that they are pregnant. I'm under a bit of stress right now and just put my cat down that I had since I was 5 and I'm just having a rough few weeks. I read that this can also make your period lighter or not come at all. Is it possible that I could be pregnant? I'm so scared and just pysching myself out. Any ideas?

If you are using both birth control pills and condoms I highly doubt that you are pregnant. I think I would just attribute your period change to stress.