Prove that the tooth fairy doesn't exsist.
The burden of proof lies on the person making an assertion. It is impossible to prove a negative.
Do you believe EVERYTHING you are told, because there's a lot of things people could say exsist, and you could not prove that any of those things do NOT exsist.
Space aliens, the tooth fairy, unicorns, the flying spaghetti monster, Bigfoot, the Loch Nest Monster, do you feel that you are obliged to believe in these things, since you can't prove they don't exsist ?
I am an agnostic, but from what I understand of the atheist postion, if there is insufficient evidence of a thing exsisting, then there is no real reason to believe in it's exsistence.
And not having an explanation for something is no reason to say "God did it". That is just appealing to "God of the gaps".
Also, I don't know which particular God you believe in, but if you are a mono-theist, then you must disbelieve in all the thousands of other Gods. Do you have proof that every other God but yours does not exsist ?