Hi! Can you ejaculate? Are there any changes from before? I do not want to disappoint you, but most likely cause is in your head. You see, the whole action and ejaculated is a very very complex event- different parts of one's brain have to function either in perfect sync or in other parts in perfect async. The parts for thinking and imagination must be perfectly satisfied with the situation, the both parts of vegetative system have to work correctly and at the correct time switch one off and the other part on (sympathetic and parasympathic systems). And all the firework of brain impulses have to reach correct nerve endings in penis, testicles and other body parts (there are but a few muscles in penis, which we can control at our will, most of them we can't control). And all the signals coming from penis and other body parts (eyes, ear, nose, skin...) have to be just right for our brain. If anywhere in this complex process is anything at all wrong, it won't work/ won't work well (e.g. she doesn't smell/look right, your big toe hurts or bad day at work). So most likely there won't be anything your doctors could see in some scans. You should visit an urologist. They can use ultrasound to search for blockages, test you on some infections or even do an endoscopy of your urethra if deemed necessary. Good luck and get better soon!