#1
Alright so I've been tuning my guitar to drop d, drop c, etc. and I keep having to re-do everything multiple times because the strings get out of tune when I when i move on to the next strings. It didn't use to do this. What's going on?
#2
Firstly, Floyd Rose or fixed bridge?

The change in string tensions will knock the strings out of tune,
So that's why some strings will go out of tune when you drop/ increase the tensions of other strings.
#3
AdamG313 asked a good question. If it's a Floyd Rose, you should either reset it yourself or have a guitar shop do so. If it's fixed, you don't need to do anything with the bridge.

However, no matter which type of bridge, I have to advise you to readjust you truss rod. If you don't, your neck will eventually warp. Here's a decent article on it. http://www.athensmusician.net/archive/2001-05-01_geneimbody1.shtml