I don't mean to be offensive. I do genuinely want to know for myself. I apologize in advance if anything comes across as insensitive.

1. How does one know they really feel the way they do?  How does one know it's not a phase? If one is only discovering this is their twenties, is that a sign that it's a phase?
2. Is it possible to think one feels male just because one wants to be one because one likes them?
3. If I used to feel strongly female (even if the reasons make absolutely no sense), does that mean I'm actually female?
4. Is it normal for gender to change so frequently? Seriously, today it was changing by the minute. I can't keep up with myself. Or am I just fooling myself? Maybe today I actually felt like nothing and was fooling myself because I wanted to feel like something. Or maybe I'm stupid and this whole thing is just me being stupid.
5. I don't like feeling nothing or feeling female. It makes me feel empty and makes me wonder if I'm making all this up and tricking myself. This terrifies me because the idea of not being in touch with reality terrifies me and the possibility of being fake makes me hate myself. I don't know what this means or what to do about it. Does anyone have any advice?

Btw, my gender changes. It's not that I can't decide. If I could decide, I would be male or androgynous. It's more like the gender I feel like changes whether I want it to or not.
That's all the questions for now, but I'm sure I'll have more later.

My advice would be to seek out a good gender therapist, they could help you figure things out.

Edge, Jaime Renee is correct.  Seek out a good gender therapist.

You might also want to look through the threads on the androgyne board

It's okay to take your time, and it's okay not to have a static definition of your own place on the gender spectrum.

As far as realizing who you are - some people felt certain for as long as they can remember, and some came around to it later in life.

I'll third the therapy suggestion, but not everyone can find a gender therapist. I used a regular therapist, and I also just did a lot of thinking and exploring and reading. Try playing with your gender expression and see how it makes you feel.

You'll meet people here who identify as bigender or androgyne who will have experiences close to what you've described.

Unfortunately, there are no gender therapists in my city and I can't leave because I can't drive. I did try talking to a regular therapist, but she didn't know what the heck I was talking about. I cannot talk to another therapist because they cost money I don't have.

I'll reiterate what Jamie D said, and advise you to examine the Androgyne board.

For me, I became fully aware of my gender identity through phases. At first, I thought I was a cross-dresser. Then, I thought androgyne/non-binary gender variant/genderqueer, as I felt that I was not a man or a woman, but something in between. Next, I felt that maybe gender-fluid was a better way to describe myself. Eventually, and with the help of a therapist, I identified as transsexual and now I'm in transition.

Currently, my daughter identifies as genderqueer. There is a part of me that wonders if this is a phase or if this is something that she's truly discovering about herself. Time will tell, and only she can define who she is.