Properly finding G-spots?

I've started masturbating recently, but when I do end up trying it out, I can never find my G-spot. I've been wondering where it really is. There is this one spot I've been pressing on and whenever I do I get this clenching feeling in my butt and I don't know if it is or isn't my G-spot. They say it makes you feel like you have to pee, but for me it's just the need to go number 2.

Another question I have is how I can fit more than 1 finger. Whenever I try to, I end up getting sore and it's really painful. I don't have lube either so it is difficult. Can I have some tips on getting used to more than 1 finger?