Erectile problems at 21

Patient: Hello, I am 21 years old, male, 5’10” and 130 lb (my high metabolism does not allow me to gain weight very well.) For a few months now, I have been experiencing some symptoms related to erectile dysfunction. I have never engaged in sexual activity with a partner, but I do masturbate fairly often. I have never had any issue before, but now I notice soft erections, slow recovery from previous ejaculations and slightly decreased flaccid length and girth.Due to some weird brain fog – like symptoms, I once visited a cardiologist and I mentioned this problem as well. I got a stress test and an echocardiogram done, and I also wore a Holter monitor for 24 hours. The doctor said there was absolutely nothing wrong with my heart or circulation.Once, the ED vanished completely overnight, and my performance was just as before, if not better. But a week from that day, it degraded again, and it has been so ever since. I am very confused about what might be the cause. I am a vegetarian, I try to eat healthy, and I am fairly active. Any suggestions/comments about this issue will be helpful. I am not taking any medication. Thanks