If you use "despues" you have to use the preposition "de" because is after doing something and if you don't use it it's like "after the shower.". not like "after taking a shower" wich is what you really mean.
ducha is like, shower, so it could be, "Yo me seco despues de mi ducha" although my type of spanish doesn't use "ducha" as much we say Ban~o but the ~ goes on top of the n and not between the n and o, but either way yeah, it would be like that
