Is what is happening considered a punishment from Allah in this worldly life for not adhering to the covenant of not speaking with young men? Is sincere repentance accepted for that? How can this covenant be expiated? Is it permissible to marry a righteous man without informing him of previous relationships?

You have wronged and oppressed yourself by engaging in relationships with non-mahram men. The need for marriage does not justify disobedience, and such behaviors may distance young men from marriage, as they seek chaste women. The aversion of suitors to you might be due to these sins: (And whatever calamity strikes you, it is because of what your hands have earned, and He pardons much).

You must repent from these relationships and not return to them, especially since you made a covenant with Allah to avoid them. Breaking a covenant with Allah is a grave matter and a characteristic of hypocrites: (And among them are those who covenanted with Allah, 'If He gives us from His bounty, we will surely give charity and be among the righteous.' But when He gave them from His bounty, they became stingy with it and turned away, being averse. So He caused hypocrisy to be in their hearts until the Day they meet Him, because they broke their promise to Allah and because they used to lie).

Despite the gravity of breaking a covenant, whoever repents, Allah accepts his repentance: (And indeed, I am the All-Forgiving to whoever repents and believes and does righteousness and then is guided). And the Prophet, peace and blessings be upon him, said: "Whoever repents before the sun rises from its west, Allah will accept his repentance."

You must conceal yourself and not inform anyone, whether a suitor or otherwise, about your past relationships, as the Prophet, peace and blessings be upon him, said: "All of my Ummah are pardoned except the open sinners. And indeed, among open sin is that a man does an act by night, then wakes up - while Allah has concealed him - and says, 'O so-and-so, last night I did such-and-such,' while his Lord had kept him concealed, but he wakes up revealing Allah's concealment from him."