My doc put me on generic Cialis a couple of years ago. No matter what a tried (2.5mg a day, 5mg a day, 10mg as needed, 20mg as needed) the results were lackluster. I just figured PDE5 inhibitors didn't really work for me. For the heck of it, I tried generic Viagra (60mg). It worked wonderfully. I used it about a dozen times since for a guaranteed high-quality erection.
So, if Cialis doesn't work for you, don't give up hope on PDE5 inhibitors until you try Viagra. You might get lucky like I did.