My Period Was Very Light This Month. So Light I

My period was very light this month. So light I only wore pantiliners and was two days shorter. Now 3 days after it ending I had light brown bleeding earlier today. I have been tested for STDs and I am freaking out BC of this. This is the first cycle I have ever had like this. Also I feel full all the time even when I'm hungry. Idk what is going on. I'm 26 in a committed relationship of four years now. Can someone give me some insight as of to what is happening to me. I guess me just being pregnant with my 1st child is too much to ask.