Whenever I switch to wield my scythe it damages me a few hearts, is this intended?

It was the diamond scythe, but I think the cause was either improvableskills or nameless trinkets because it stopped happening after I removed those 2 mods.

What Scythe specifically? This is probably not Simply Swords' doing.

My guess is that you have a mod that adds attributes to gear, such as TierdZ or Gearifiers.

Oh, you had already provided the type of Scythe in the title. My mistake!

I think you're probably right. I'm not familiar with either of those mods, but the base weapons from Simply Swords are almost entirely vanilla swords in terms of code, so unlikely to be a cause.