Umm.. yeah, i bet if the state heard what you did, your kid would be taken from you and you'd be investigated for child abuse. That's not an appropriate age for spanking. Chances are he feels degraded, humiliated and angry... more than he feels regret. When you discipline a child the consequence should not be so over the top as they forget their wrongs and focus on the wrong you're doing to them. Punishment of any kind should never be given in anger. My parents handled things great when i did something wrong, they would initially give me the scolding i deserved, haha, then send me to my room. They would calm down, discuss my punishment, and then come in and tell me, or spank. Of course spankings stopped before i was a teen. And when i was spanked it was never done while they were still angry. And it was never so bad i had to sleep on my stomach naked. When you take it that far, you aren't punishing the child, you're taking your anger out on them.
Yes, the bible say spare the rod spoil the child, but that does not mean hitting or beating your child out of anger and leaving bruises, or making it so painful they can't even touch that spot hours later. Or that clothes are painful. Thats just mean and abusive.
Also, a major part of discipline most parents miss is the last part. The reassurance to the child that despite their failings, and though you had to punish them, they are no less loved or cared for. People think true discipline ends with the punishment, when it should actually end with a hug and an 'i love you'.