May I ask why you want to do this "naturally?" I know this isn't what you want, but would it be possible for you to get to a salon and have some professionals suggest some gentle ways of lightening your hair? I feel like they'd know better.
I'm wary about using lemon juice. It's really bad for the skin. If you keep lightening your hair over and over again, you're going to do some major harm, especially at the scalp. Lemon juice is very acidic and irritating and can cause photosensitivity over time. I'm not as familiar with the effects of lemon juice on hair, but I'm also worried that it will either not cause any significant changes, or will make the color of your hair brassy or something like that. Overtime, it'll definitely make it super dry. I'd honestly imagine it to be more damaging than bleaching your hair in the long run.
I don't know much about haircare and lightening hair, admittedly; my knowledge is more so with skincare. You definitely should not get it anywhere near the skin. I have never heard about using chamomile water, but I'd really recommend doing some heavy research if you want to try it; natural doesn't always mean "better."