That is both interesting situation and my first thought was that if you had prostate surgery it could have been the cause. Yet if you can ejaculate when you masturbate then it is not the issue. I would be candid with my Urologist and you should be able to gain meaningful insights. In the interim yoga could help!
If all medical suggestions are exhausted one can take help from kundalini yoga. One can find subject of BANDHAS ( yogic energy locks). If these three locks are exercised In the form of MAHABANDH, one may get rid of many sexual problems. This exercise, enhances circulation of groin area,normalizing the function of sexual orgasm.
Breaths to reach Orgsm is also a good technique in which your are asked to breath in three different ways. A couple can exhale and inhale simultaneously, alternatively and in a circular fashion. Google these words and find details. I understand you do not need deep knowledge of yoga to learn the above for the specific purpose.