No morning wood on Propecia. Is this a concern? Should I quit?

This is certainly worth a discussion with your physician. The long term side effect are not clear and everyone responds differently. Personally, I never prescribe Propecia to anyone of child bearing years. 
Alternatives such as PRP, though more expensive in the near term, in and of itself is completely safe and with periodic maintenance treatments offer an attractive substitution. 
Exosomes, due to their more robust nature have become my new favorite. The safety profile is excellent, results superior, maintenance treatments not required as often. 
All the best in finding a solution that works for you.
Warmly,
Arbella Sarkis, MD

The decision to go forward with finasteride should be made with the doctor who prescribed it to you so contact your doctor