Try to find out what makes you without normal erection, but most of the cases are because of pressure or illness. Having a happy life can improve your erection, if you can't erect out of the sex life, try to ask the doctor.
get your prostate checked, may need to get on some kind of supplement for your prostate. since the pill works good for you, it is probably prostate related and it is normal for the prostate to enlarge as you age, which can lead to the problem that you seem to be having.good luck!!
perhaps you sohlud see your doctor. it may be psycological or due to an ilness you didn't know you had. I'm sure your wife wants you fit and healthy (not just in the bedroom).
It is also possible you do need to spice up your love life, but really that just means making a bit of effort rather than sticking to a routeen.