Whats Going On?!?

K, so im on birth control... Have been for about one month, I am now on the green (sugar) pills... So far I haven't gotten my period, its really got me worried. I took my very first bc pill the first day of my cycle (which was on january 4th). I was told that I wouldn't necessarily get my period within the first day of the green pills, ok, so I accepted that. Last night I started to bleed at work, and was really happy about it, cuz all the pregnancy worries went down the toilet... Now today im not bleeding at all, and im soooo stressed about whats happening to me! I thought for sure what I had last night was my period, I had all the signs, I was cramping and just felt like I was on it.. I find myself crying because I don't know what I will do if I am pregnant. So what was this 'spotting' thing all about last night? And when would be the earliest I could take a pregnancy test? Do I go by when my last period was, or when im on these sugar pills? Someone please set me at ease!!!!!