My hand started hurting after a long practice of guitar?

Take a break. It's mandatory.

Your individual muscles in your hand are getting used to you playing the guitar. It took me a year from when I took up the guitar and the keyboard for that to stop. I would relieve my hands by massaging them with the other. It helped the pain and loosened them up. You are giving your hands a new kind of exercise and after a few months they will be used to it, and stronger besides.

Wow - that's a really L O N G sentence.

From what you say, the only suggestion I could make is the obvious one: that spending four hours working on barre chords caused some kind of damage/strain/stress or whatever to the muscles/joints/tendons/nerves etc. in your hand. It seems unusual that the pain started afted you'd finished playing.

If I was you I wouldn't try anything like that again until the pain had gone completely and then I'd get back i to playing barre chords very gently and very gradually. Apart from that, the only suggestion I could make would be to seek medical advice if the pain continues.

Good luck.

Added, please ignore any comments suggesting that your pain is normal or that you are "getting used" to playing barre chords. It's not even a case of your muscles being tired or stiff. If you are in pain a week after stopping playing then something is wrong.