What Causes Short And Scanty Periods?

I usually have a 5 (rare) to 7 day period. I just had a lighter than usual 2 day period, and just slight spotting on the 3rd day (today). I also drank a couple of cocktails last night, but have the worst hangover. It got worse throughout the day. It feels way worse than it should for what I drank. Could I be pregnant based on these symptoms? I recently started taking new medications, because my emotions are out of control. I have been through a lot in the last few months, so that may not mean anything.

Thanks in advance.

lmc