The first month of medical school is a very strange time. All the different cliques haven't formed yet, so people who usually would never give you the time of day are suddenly overly friendly to you. Of course the cliques will eventually form, but until that happens, you can expect your new classmates to do weird things like inviting the entire class to barbeques and house parties. You will probably find this really unnerving, because you really don't want to hang out with the alcoholics but at the same time you don't have a reason not to. Fear not, soon every group will remember how much they don't like the people in the other groups and everything will go back to normal.
Class is also easiest during this first month, so go ahead and allow yourself to have fun. You might as well go out to all the class-wide parties, because you sure as hell won't once school really ramps up. You might as well get your fill of it while you can. Also, make sure to hook up with that cute guy or girl. This is definitely your best chance to do it, because people in unfamiliar situations have an uncanny propensity for making poor decisions.
If you are totally insecure about yourself and want to try hanging out with the cool kids for once in your life, you should try to take advantage of this month.