What Causes Sharp Pain At The Head Of Penis Radiating To The Shaft?

Hello, my husband has experienced constipation within the last two weeks, as a result, did a lot of straining. Now, he is experiencing sharp sporadic pains from the head of his penis down the shaft. Can you please educate me on what this might be. He has the desire to engage in sexual activity however, he is unable to keep a full erection, meaning he ejaculates on a semi-soft penis. Your expertise is desperately needed.