@ambitiousDrum3600
Some very common reasons besides changes in medication are, changes in arousal, lubrication, techniques/position/etc, distractions/setting/scenarios, alcohol consumption, worries about birth control, worries about duration so partner achieves climax, too much focus on performance instead of arousal.
Now more recently people also worry about Covid-19 related things too, including getting infected due to close contact and financial and job worries.
Any of those things might require communication to help resolve the issues.
Here are some resources and ideas one might consider.
Resources one might consider: search the web for relevant topics like these
Regarding arousal:
https://www.psychologytoday.com/us/blog/shameless-woman/201212/put-your-attention-sexual-arousal-not-orgasm
https://www.google.com/search?q=%22AROUSAL+TEMPLATE%22
Regarding male performance:
https://www.google.com/search?q=diagnosing+male+sexual+performance+problems
typical results:
https://www.medicinenet.com/sexual_sex_problems_in_men/article.htm
https://weillcornell.org/news/5-facts-all-men-should-know-about-sexual-problems-and-dysfunction
Resources regarding performance anxiety:
https://www.google.com/search?q=male+sexual+performance+anxiety&oq=male+sexual+performance+anxiety
https://www.psychologytoday.com/us/blog/what-would-aristotle-do/201105/some-tips-overcoming-sexual-performance-anxiety
Ideas one might consider:
Identify ALL of the ways things changed since the problem started.
Besides changes in medication, what other things have changed? Especially focus on what has changes regarding arousal for him and also you.
For example, changes the relationship, changes in thoughts or worries of any kind, changes in expectations, changes in techniques, changes in hygiene, changes in birth control, changes in lubrication, changes in the setting, changes in distractions, changes in pressures of any kind.
Think of everything that might be relevant.
Consider going back to the way things were before the problem started in as many ways as possible.
Focus on arousal more than reaching a goal.
That's all I could think of. They are just ideas, not diagnosis, not recommendations.
Please forgive any typos above.