I Think it may be down to your body being used to the ejaculation. Ive had the same problem too but if you stop it for another few weeks, it goes back to normal.
Hi,
How is your general health? Do you have any known disease?, may be you should get a general health check up by a physician. If nothing wrong and if you feel tired and exhausted, all that you need is to take balanced food rich in proteins, zinc and other micronutrients. If you want to know more about Recommended Daily Intake of variuos nutrients, just Google for ' FDA RDI Macronutrients' and get more info on that.Also Google for 'Zinc and male sexual health' you will get a heap of info on this humble trace element and its vital role in keeping up male sexual health.
Solace
have you had any change in routines since then? food, daily routine, meds, ect?