I use the Wilton recipe for my buttercream and everytime I make it the exact same way - same icing sugar, butter, shortening etc. And sometimes it is sweet sometimes not and sometimes its WAY to sweet. Why is this happening when I am using the same everything and the same amounts?
Do you use salted or unsalted butter or mix it up?
Is it too sweet once on the cake or out of the bowl?
Different flavor combo's of cake/filling can make the buttercream less/more sweet.
For example a tart filling will offset the sweetness of the icing as opposed to a sweet filling which may make the icing seem even sweeter then it really is.
I use salted butter only and the odd time that I do have unsalted for a recipie I always check to make sure.
If I get my icing from the bulk barn I weigh the icing sugar out in 1 lb bags and if I buy it from the store I buy the 500g/1kg bags.
At first I thought maybe it was the filling also, but this last cake I filled it with a small amount of the buttercream I used under the fondant and it was still really sweet.
if its only a recent thing, probably one of the brands you use has changed something in its makeup.
if it is too sweet then u can add a little popcorn salt.
however, it may be your tastebuds that are playing up - the things you have eaten and drank before can affect how things taste for a while afterwards. plus, if like me, u eat a fair bit of what you make, you can come to be fed up and not like it - for whatever reason that you only now notice.
it may just be time for you to change the recipe you use. although, u are not clear if you weight all your ingrediants or just the sugar. it will make a difference!
xx
Honestly, I find the Wilton recipe is ALWAYS sickeningly toothachingly almost-disgustingly sweet, so how it could ever be not sweet is
Oh sheesh. That's the recipe I started with way back when. Thank god I moved on! OP-I would suggest experimenting with different recipes, change up the game a little, bring some fancyto your offerings! 
Here's the recipe I use all the time and it tastes SO much better than Wilton's. Crusts very nicely too. It's originally from a woman who goes by the screen name "bunnywoman" on the Wilton website.
Ingredients
1 cup shortening
1 cup butter - softened
1/3 cup luke warm water
1 tsp popcorn salt
1 tsp clear vanilla
1 tsp almond extract
1 tsp butter extract
2 lb bag of powdered sugar
Directions
Cream together the butter and Crisco until nice and fluffy. (Speed 6 if you use a Kitchenaid.)
Measure out the luke warm water in a standard measuring cup and dissolve the popcorn salt in this water.
Add the flavorings to the cup. Stir it up well with a spoon.
Turn your mixer speed to the lowest possible setting and add in the powdered sugar slowly. Alternate back and forth with the water mixture. Keep the mixer on low until all liquid and powdered sugar are combined.
Once combined then turn the mixer up a notch and mix well. Approximately 2-3 minutes.
I realize it only adds salt, butter extract, and almond extract, but it tastes quite different. I think it's the almond that makes it taste so different. And the salt cuts some of the sweetness.
Maybe Wilton has changed their recipe since I last bought one of their yearbooks, but butter flavor and almond flavor were both in their recipe. Shrug.
I use Buttercream Dream BC receipe from this site. But instead of 5 TBS. of milk, I use heavy whipping cream. Yummy.
MBC = ?
Sorry I'm new to all of this. I want to try to different recipes and some of the more fancy ones - which ones are most recommended?
Thanks everyone for your help also 
They are the most decadent, silky, delicious icing you've ever had. It's a grown up version of buttercream, let's just say that. No powdered sugar, no shortening, no imitation extracts or flavorings, no greasy slick on the roof of your mouth.....it's heaven. I use SMBC exclusively. The first time I made it, I thought I died and went to heaven. There are plenty of recipes out there, but Ifollow the Well Dressed Cake version, found in here.
Quote by @%username% on %date%
%body%