Can't go poop! Please help ASAP!!!!?

So it was Friday when I drank more than I have drank in over a year, and on Saturday I felt like not eating anything all day. It was not until Sunday at noon where I threw up and also could not go poop. My behind felt like there was a cut in there because every time I tried to go it stung for some reason. It is now Tuesday and I still can't go. Well I can but it's just little tiny turds. Also I still am having minor stomachaches and headaches. How can I go back to being normal? HELP!!!!!!!