Is it normal that i always have stains in my underwear?

Don't wear underwear.

Could be related to your anus (hemorrhoid?), consult doctor.

I always have skid marks or little turd balls in mine

Maybe you sweat a lot. My cloth are wet a lot just from sweat.

you need more air up in there.

Sorry
I thought you were a guy

I had the same problem
Solution : I started wearing boxers
Problem solved.

I've heard of this before, so you're not alone, though I don't have this kind of issue. If you are concerned about this, however, as recommended above, I suggest you seek medical help.

What kind of stains are they?

Eee.

Whatever you do, don't wear thongs! Maybe you have hemorrhoids? Get plenty of fiber in your diet to prevent constipation. Constipation can make hemorrhoids worse thereby causing increased inflammation in anal area which makes it harder clean when you wipe. Then later when the swelling goes down and you start to sweat your ass will itch and if you scratch it *poof* you get those dreaded skid marks!

It is probably your underwear. Wear something lighter or a larger size and see if that helps.

wearing cotton underwear lets that part of your body breath better

Lolwut anal leakage??

Man, use period pads. They work fine if you sweat a tonne and you've recently shaved your ass.

I don't know your gender, so I'm not trying to be mean. Wear a pantyliner (not pad) for now. It's probably not a big deal. Next time you see a doctor, ask about it.

it could be sweat, sometimes when i go to gym and i sweat when i sit down in a chair it'll be wet with sweat its normal

Has your diet changed? Maybe you need more fiber.

I agree with both michaels4p5 and GreyWulfen. Try wearing something maybe of lighter weight(it could be the material), or get a size a little larger.

You're possibly wearing too tight clothes.