[BLENDER] Weird marks on a model

So I am currently making a model on blender and I am getting these weird marks on the model whenever I shade it smooth.
This is the picture beforehand:

And this is it after:

Is there a way I can smooth the object without these weird stretch marks appearing? Also, just a little information that might help, I used a boolean modifier to cut the mesh which might have done something to it.

If there is another way to cut an object or smooth an object without these marks, please tell me. Thanks!

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When dealing with smooth shading on objects with 90-degree edges between faces like that, be sure to select the edges and go to Edges > Mark Sharp. You will then want to go to Mesh > Normals > Reset Vectors after manipulating any normal data.
It would also help to cull unnecessary vertices; from your screenshot it looks like there are multiple vertex points along the straight verticle edge. You can clean it up manually or try Mesh > Clean Up > Limited Dissolve.

Limited dissolve worked perfectly. Thanks!