Certain factors may contribute to this :
>Abnormal hormone levels
>Abnormal levels of brain chemicals called neurotransmitters
>Abnormal reflex activity of the ejaculatory system
>Certain thyroid problems
>Inflammation and infection of the prostate or urethra
>Nerve damage from surgery or trauma
>Stress. Emotional or mental strain in any area of your life can play a role in premature ejaculation, often limiting your ability to relax and focus during sexual encounters.
After checking with your doctor about the causes and after a physical examination the doctor may prescribe a medications that may delay orgasm some are used for this purpose, including antidepressants, analgesics and phosphodiesterase-5 inhibitors.
These medications may be prescribed for either on-demand or daily use, and may be prescribed alone or in combination with other treatments.
>talk therapy, involves talking with a mental health provider about your relationships and experiences. These sessions can help you reduce performance anxiety and find better ways of coping with stress.
>Counseling is most likely to help when it's used in combination with drug therapy.
so check with your doctor and better a urologist for further investigation your doctor may order a urine test to rule out possible infection. If you have both premature ejaculation and trouble getting or maintaining an erection, your doctor may order blood tests to check your male hormone (testosterone) levels or other tests.
However ,if this premature ejaculation is felt occasionally in certain situations or being tired or stressed then no problem try to change your routine and have more rest periods .