OP, your career is not over. Yes, you have some uncomfortable conversations ahead of you, but this should not completely derail your chances for medical school. You've already gotten some great advice and perspective in this thread. I'll add few thoughts/suggestions for consideration:
1) Don't do anything for at least another semester. This is all pretty raw for you, so give it some time and space before switching majors or making any other firm career plans.
2) Tell your parents. It will suck, but take responsibility and own up to it and tell them about it face to face. You've made a mistake, welcome to the club. If you become a physician, you will have to do this a lot more than you realize - telling your fellow residents, attendings, even patients when you've made a mistake. It always sucks, but it's the right thing to do. While this is hopefully the last time you cheat, it won't be the last time you make a mistake.
3) Agree that applying after you graduate is probably the best option. Yes this means a gap year but it will go by pretty fast while you're busy applying to medical school. The job you get for the year doesn't really matter, it's just temporary.
4) Taking a little extra time will allow you to spread out difficult classes a little more and devote a little more time to the MCAT, hopefully resulting in better grades and a higher MCAT score.
5) I might be a contrarian and suggest focusing on medicine if that is still your goal. If there are small change you can make now that will facilitate other Plan Bs, then sure, that's fine, but I wouldn't go throwing everything out of whack just yet. Select a major that you like and that will allow you to make As and take the required pre-reqs for medical school.
There's nothing guaranteed in all of this. Statistically you had only a 50% chance of acceptance even before this whole incident; if those odds weren't enough before to make you change majors, then I would sit tight for now. Agree with taking on responsibilities that show you've grown past this, and lets not forget that the growing hasn't actually happened yet. Growth is usually not any fun and comes with some awkwardness and discomfort along the way.
The truth is, if you come through this and have the scores and academic chops to handle medical school, I think I would prefer an applicant like you who has made a mistake like this and suffered for it over someone who just never got caught. Dishonesty is a HUGE problem in the medical field. Do you have any idea how often I'm lied to by other physicians? How often I see physicians lie to others? ALL THE TIME. Daily. It happens so often that I almost don't notice it anymore. They're never big lies, just little ones that people tell almost by reflex to cover for things they don't know or haven't done. Lots of "I think" that test result was X or "I believe my exam was Y," often accompanied by the sounds of frantic clicking while they try to look up what was just asked. If you come out of this the sort of person who will never pull crap like that, then I'd vote for your admission any day.
Now go talk to your parents.