Is the occasional feeling of sadness and distress due to problems that occurred during the engagement and on the wedding day a result of having known the wife before the engagement, and could this sadness be a trial from Allah for repentance from previous sins?

Affliction does not necessarily mean punishment for a sin. The Messenger of Allah, peace and blessings be upon him, was the most afflicted of people, yet his sins were forgiven. Problems may simply be a trial, and enduring them patiently leads to good outcomes. One must hasten to repent from sins, for repentance is a cause of divine success and Allah's love. Furthermore, one should overcome the past and conquer the whisperings of Satan, who seeks to sadden humans, and look forward to the future with good expectations of Allah.