At least you are honest yourself and - unlike many others whom I've run into - don't pretend that you are excited for something that isn't truly that exciting. I know a lot of people who will pretend that they actually enjoy sitting in bio lab for 6 hours using a pipet in fear that if they don't act 100% excited about it, they won't make good doctors or something.
I agree that medicine is starting to not look so great for me as well, for a few reasons:
1) It requires more schoolwork, more classes, more needless competition, etc.
2) It entails a life of toiling (which makes a simple 9-5 job look pretty nice)
2) Most doctors (whom I've met) don't seem to love it too much
3) I don't like most of the other people I see going into it
That said, please don't listen to people who say "Well if you are losing your passion for being a doctor, you better reconsider." Perhaps you should reconsider, but not based off of some loss of a nebulous "passion" (a word that doesn't really mean anything). None of us can really know for sure whether or not we will enjoy or have a passion for doctoring, because we haven't been doing it for 20 years.
I think for the time being it would be best to look at the realities surrounding your situation. Think about what truly drew you to medicine: is it academia? money? people? job security? An (as always) be honest regarding the reason. If you find that you can get those things with some less intensive line of work, then perhaps you should reconsider (I am in the process of doing that right now). However if you have needs that are only satisfied by a job in medicine, then put up with it in hopes that things will get better.
Another good (though slightly negative) thing to do is to look at the downsides of other fields of work. Surely they all have their crappy aspects, and maybe considering those will make you feel better about going into medicine. I actually am an engineering student, and used to be really excited about it until I saw how lonely, cubicle-like, and transient most of their jobs are - unfortunately that is the prevailing reason for my wanting to go into the medicine (it is another "version" of hands-on, applied science, but provides a much more dynamic environment).
Another thing to consider (which a lot of people here seem to forget), is that - as cliche as it sounds - you aren't defined by your line of work. Too many pre-meds make the mistake of feeling like their future and persona are competely dependent on their major/career/etc. But really people are people, and most people won't end up deriving happiness from their line of work anyway (personally I think happiness comes primarily from interactions with friends/family/lovers). So... you know, don't fret too much over the decision, you'll still be the same person (and probably end up happy regardless).
I know this post is kind of meandering, and it is hard for me to give you a single punch-line of advice. But continue to be realistic and honest with yourself - don't think so much about all of the philosophical "dream" and "passion" crap that floats around here. If you can't come up with a decision, then try to get a deferral and try something else for a year (go see the pyramids or something - I don't know).
I hope that helps. Don't feel bad about your doubts - it is good that you are having them; it's the doubtless ones ("I know for 100% sure that I have a passion for medicine) who are obviously clueless.
