Ok so my question is.. how to I prevent bulging after I’ve layered and frosted my cake? I’ll frost my first layer and set the next cake on top and then frost the whole thing but the next day after it sets you can see the frosting bulging in the middle so then my outside layer of frosting isn’t smooth anymore! I need some advice! 

Usually when that happens, it is because air has been trapped. Do you let your cakes settle for a few hours, or overnight before doing the final layer of icing? I usually use a lolli stick to poke a hole in the top of the cake so the air can find it's way out. If air is trapped, it goes out, and pushes the icing outward basically. 

I press down each layer as I go. 

I lay down cake layer, add filling to it, put next cake layer on top, take something flat that is larger than your cake layer (I use my acrylic boards) and gently but firmly press down, repeat until tier is filled.

I imagine you possibly have either too much icing in your layer or that it is too soft.

The only time I've ever experienced this is when the cake is left on the counter over night and not refrigerated.  The best solution for me it to keep my cakes cold.  

I have heard of using a ganache dam around the outer edges of the layer and fill inside with buttercream.  Also, doing your crumbcoat in ganache makes for a sturdier construction and will help with bulging, as well.

Besides what has already been mentioned, be sure you have not put too much filling it.  It is  better to use 3 layers of filling - and only a smear in each - then to use one between the 2 layers.   When you make your dam use a tip 12 (and for some, rather hard pressure), then do not fill above that line.   My pressure must be great as I've seen others squeeze and only get a rather thin line:)  When I make my dam w/tip 12 it is about 1/2" tall :)