How can it be that he ruled for three years? After he died, Asa became king in Yaravam's 20th year!
Rashi (Melachim I, 15:9): Aviyah's third year is counted towards Asa's reign, and also towards Aviyah's reign, so Aviyah reigned three years. 'Rashi' ? Aviyah ruled less than three full years.
Radak: I mentioned above (verse 1) that Rechav'am ruled for part of Yaravam's 18th year (and he died, and Aviyah became king immediately). That year was counted towards Aviyah's reign, so he reigned three years.
Why does it give his mother's name?
Refer to Melachim I, 15:2:1:1.
Here it says that Aviyah's mother was Michayahu bas Uri'el. Elsewhere, she is called Ma'achah bas Avishalom (Melachim I, 15:2) and Ma'achah bas Avshalom (above, 11:20)!
Refer to 11:20:1:1-2 and the notes there.
