Why does my skin hurt? There's no rash or marks. It just feels like my skin is one big bruise. My skin all over is so sore and theres no cause

See your doctor. There could be many reasons why this is happening. I would recommend an evaluation by your doctor so he/she can run tests to evaluate for possible causes.
Biopsy. A biopsy and blood tests may be indicated to look for underlying problem which os causing symptoms. See dermatologist.