It could just be your feet! I have the same problem, so don't feel bad. Maybe your friends just aren't complaining about their feet because to them looking fashionable is more important? I know people like that :S I had a friend who would wear flats that made her feet bleed because she said that if she kept wearing them it would stop.
It didn't stop and she just ended up having cuts on her feet. I would rather find a pair of shoes that fit well than deal with that.
I have the same problem. I am a half size, this might be why your shoes are falling off. Try another size or find a place that has half sizes. Now here is the frustrating part; not every place is going to offer half sizes. Typically what happens is they tell you to go a size up. This doesn't always work for everyone. Best thing to do is to just go out and try on as much as you can. Find styles and stores that have shoes that work best.
Everyone's feet are different and even two feet on the same person can be two different sizes! It can be a real pain in the butt when trying to find cute shoes, I know all about this! I have wide feet - well just wide where my toes are, my heels are narrow! My heels pop out of every shoe!
You may even have to spend a little more or add inserts to make your flats more comfortable. Flats don't typically offer much support, so this might be why you are feeling pain. It's not good for your body or your feet to be walking on nothing all day. Get some good inserts to support your feet! It will help stop the pain and prevent food damage.
First off, it is very important to wear foot ware that properly fits. It supports your body weight and in general made to cushion the heel, support the arch as well as the toes.
Second point of contention. You are not your friends. They are not 'just like you'. you could be flat footed, your arches could be collapsing due to no arch support. From the lack of proper foot ware with the proper support you could have shin splints.
Granted they may look cool or trendy and feel okay for short periods of time but they are made for a specific purpose. Have you ever looked at the feet of the 'professionals' that wear these all the time...even though you might not be dancing like they do, your feet take a beating as it is everyday and wearing these for day shoes will not help your feet in the long run.