Does anyone know why my carrot cake is doing this?

I think you need to be a little more specific????

yes 

but did you use fresh carrots? did you squeeze out the juice first? did you use pineapple? those are very very liquid filled ingredients -- or it could be from the buttercream -- yes more info is needed

As the other's said, what exactly are you meaning it is leaking?  Pictures would hel;p a great deal.  We;d like to help you but do need more info.