I'm new to the site, and after reading many stories I thought I'd post my own. What I've experienced is neither as amazing nor as definable, but I think it's worth mentioning just to see if it sounds familiar.
I've had them as long as I can remember - short snapshot memories that hit me in the middle of the day. I use the word "memories" because that's what it feels like, but the important part? While these snapshots are too short to make out anything specific, I know they aren't my memories. An example: I was taking a history test last year (and being a history nerd, I was having a great time) when I got this image in my head, accompanied by a little snippet of sound and even some sensations. I saw two kids sitting on a back porch, playing with water balloons. A man stuck his head out of a window and said something. I was aware that it was hot and dry, like August in the South. For about two seconds I saw, and more importantly felt, this scene, and then it went away. I've actually had this particular snapshot multiple times; I always come out of it feeling a bit nostalgic. Other snapshots include a cat playing in front of a fireplace at Christmastime; something involving fog, but not in a creepy way; and walking around a farm on a sunny morning.
It may or may not be useful to mention that until this past summer, when I underwent surgery to remove it, I had a tumor on the back of my brain. Interestingly, I haven't had any snapshots since the surgery.
In addition to the miniature visions, I am also a number-guesser for lack of a better name. The first instance was in the second grade - my friends and I were reenacting Land Before Time on the playground, and two of us wanted to be Ducky. A third girl said, "Guess what number I'm thinking of, and the closest will get to be Ducky." I won, but the girl was a bad sport and called a rematch. I won again. And again. And again. I just heard the number in my mind. It wasn't a voice, but an unexplainable feeling. It still happens occasionally during guessing games. The weird thing is, it's only with numbers.
And unfortunately, it didn't keep me from failing high school math. ^_^
I can not explain why ti only happens to numbers, But I can suggest that you may feel secure with the numbers that you feel or hear, so the only answers you want to hear are the numbers. So, I would suggest to have faith in yourself, and be more open to the world, other than the numbers. Feel and hear the world in other ways. If you have the confidence and the faith to do this, then I think that you will hear and sence more than numbers, but events, emotions, thoughts etc. This is really amazing, trust me. You feel that you can help others with your gifts.
Just trust yourself and feel confident to pick up more than numbers, you can do it.:)