I Have Not Been Pooping For The Past 3 Days.

I have not been pooping for the past 3 days. Then one day i didnt eat lunch and when it was dinner time i drank a beer without eating dinner the next day my head hurts maybe bcs of hangover and stuff after that i cant take any foods because i just vomit. The next day my stomach grumbles even of i just eat a piece of fries and my poop is like brown water. My stomach keeps grumbling. Whats happening? Please help.