You don't need to worry about cancer.
This lump has different character.

Does the lump look like a large pimple at the bottom of the tailbone, just above the crack of the buttocks?
Does it look red and swollen?
Is a pus draining from the lump?

yes to the first two questions.
its not draining it feels like it wouldnt pop or anything, the swelling has gone down and it feels smaller.
could it just be a sweat gland or somthing?

The lump you have is called pilonidal cyst, is common for young men your age (their usual position is slightly to the left side, as in your case, and the peak incidence of Pilonidal disease is between 16 and 26)
When the cyst becomes infected it is known as pilonidal abscess (swollen, red and filled with pus)
This lump can vary in size and hurts when you press on it - if it's infected it will hurt a lot (any movement seems to make the pain worse).

Since the size of the lump has decreased, the abscess has probably drained a little.

Have you noticed that the skin in that area has been itchy?
Are you prone to acne?

Try to sit in a warm tub to get the pain alleviated.

Best wishes!
Marija

DEFINITLY a pilonidal, research it and go to a doctor, or go to general surgery but you would need a refferal from a doctor anyways... Oh and by the way i'm an overweight girl with a lot of hair XD but even if you aren't you can have one, yes it's more common for men but women get it too try to either sit up really straight or on your oouter leg message me if you have questions!

I am 22 and also woke up yesturday morning with as you decribed a "Pilonidal" At first i thought it was a bruse from sitting on my floor for ages.

Apparently tyou have from birth but only come once triggered.

Everyone says to completly remove as draining only last for a year or so.

Without sounding nasty - To leave a scar in your crack isnt a noticable place.

i am worried and dont want to hassle but im sure it'll be fine soon.