Rashi: I regret my abominations. Radak - this was after I repented. Teshuvah is complete only if he regrets his past deeds - "Mi Yode'a Yashuv v'Nicham" (Yo'el 2:14).

Sha'arei Teshuvah (1:11, 18): After I was afflicted, and I repented, afterwards I retracted [and regretted my sins]. The primary Teshuvah is bitterness in the heart.

Malbim: Now that You try to make me repent via afflictions, also when I repent sometimes amidst affliction, afterwards I regret the Teshuvah and return to my evil way.

Rashi: I contemplated and perceived that I transgressed.

Radak: After I thought about the evil deeds that I did, and recognize that they are great evils, I hit my thigh, amidst pain, mourning and shame over my deeds.

Sha'arei Teshuvah (1:18): My sins were known to people and publicized. Therefore, I mourned [over my sins] through actions seen to people, e.g. hitting my thigh. One who sins in public is Mechalel Hashem, so he must mourn over his sins in public to be Mekadesh Hashem!

Malbim: You afflicted me a second time ¹ .

Radak: Kelimah is more than Bushah ¹ . We find also "Boshu v'Gam Nichlemu" (Yeshayah 45:16).

Mesilas Yesharim (Perek 23): When one contemplates our obligation to Hashem, and how much he abandons and slackens in it, surely he will fell Bushah and not be haughty; he will be Nichlam and not raise his heart.

Rashi: My enemies can shame me for the sins of my youth.

Radak: When I recalled that what I bore and suffered was "Cherpas Ne'urai", i.e. due to the evil deeds of my days of Ne'urim, it was shame and scorn. Ne'urim is a borrowed expression (here, it does not mean youth). Just like Na'arus is before Bachrus (adolescence) and old age, so here it is earlier days. The same applies to "Chesed Ne'urayich" (2:2). Also Yonason translates like this.

Malbim: I still bear shame for the sins of my youth, for I did not fully repent from them. Since afflictions do not help, it would be better that You make me repent via showing to me Your Elokus, like You did in the past!