Ok, it seems like the problem is solved in my iPhone! After I did the restriction thing Jen139 posted above, the camera was still freezing, so what I did was a soft reset, and then the camera started working! No worries, no data will be lost with a soft reset.
To do a soft reset, all you need to do is:
1. Turn the phone off by pushing the sleep button for a few seconds, and then sliding the power off button that shows on the screen.
2. Once the phone is powered off, push and hold both the home button and the sleep button, at the same time. Release them when the apple appears on the screen. And then wait until the iPhone re-starts.
In my case, once the iPhone was back on, the camera was working normally! It has been working for about 24 hours now without freezing, so I guess it's finally ok!
Of course, now I found out another problem... my iTunes songs won't play... gonna look for a solution for that now... 😢