several factors influence on good erection,the following lifestyle changes may reduce the risk of erection problems (erectile dysfunction):
-eat healthy diet ,avoid too much junk food and unhealthy food ,eat a balanced diet(|protein ,fat and carbo) ,eat fish 2/ a week
-Limit alcohol or eliminate alcohol if it seems to interfere with erections. Even small amounts of alcohol can result in erection problems.
-Stop smoking. Smoking interferes with the ability of the blood vessels in the penis to relax and allow blood to flow in, which can affect your ability to have an erection.
-Check your medicine. Many medicines can cause erection problems
-Lose weight, especially if you are obese.
-Relax. Worrying about sexual performance may only make erection problems worse.
-Reduce stress. A heavy workload or stressful job can reduce your interest in and energy for sex.
--over sex or over masturbation could affect this ,for normal healthy erection 2-3 times aweek
SO it is normal that sometimes you feel normal erection sometimes no ,because many factors can influence ,such as sleep disturbance ,tired day ,stessfull day ,.... dont be disappointed that is norma