Trying to figure this out

I am trying to figure out whether I'm heterosexual or bisexual and I don't know how to do that.
Up until a few months ago I have always thought of myself as being heterosexual and I don't know how or when this changed but here I am today, uncertain and confused.
The problem is that I just don't know if I like women as well. There are days when i think "yes, definitely, where's the problem?" and there are other days when I don't feel that way at all. I am really confused and a bit annoyed by myself because I can't seem to figure this out. I keep thinking "this is something about me so why don't I just know?".
I know that this probably just needs time but it frustrates me not to know something so personal about myself.
Can anyone think of something I could do to make it easier to figure it out?

 

It's good to hear that other people have this problem too. Thank you! (I mean, I knew I couldn't be the only one struggling with this but it's still good to hear!)

I have asked myself those and other questions and it's easy to imagine agreeing to go out with someone or making out with someone but in reality, at the moment, there is no one I know who I would want to do that with (neither male nor female). It's hard to explain but in my mind it's easy to imagine a situation where I would be happy to kiss a woman but I don't know if that could happen in real life.
I sometimes look at strangers on the bus or in the streets and ask myself "would I make out with him/her?" but it's hard to answer because I don't know those people and I don't have feelings for them. I guess it's not exactly the best method to figure out what I want.