Many men notice changes within themselves, ranging from fatigue, depression and irritability to reduced sex drive and impotence, after they get to the age of 40 years.
The term ‘male menopause’ has been coined but rarely is there a drop in testosterone or other male hormones in the bloodstream. Replenishment with testosterone may increase sexual interest somewhat but most other symptoms are unaffected. It is more likely that stress combined with arteriosclerosis accounts for most of the symptoms.
See Stress and Arteriosclerosis.
Increase exercise and relaxation/meditation techniques.
Consider the development of food allergy and be tested.