Tailbone pain and urinary symptoms?

My husband would probably kill me if he knew I was posting this here, but I know he’s concerned about this and Google isn’t helping much.

About two weeks ago, he got a bit curious and penetrated himself with one finger anally. He did this for a few minutes and nothing alarming occurred. I asked him later if he felt anything and he says he felt a bump. His prostate, we’d assume. I asked him if it was about the size of a walnut and he said that sounded about right.

A couple days after that, he began having sharp pains in his tailbone. It comes and goes and worsens when he bends over the sink in the morning to wet his hair. Other times it’s just a dull pain. He has not injured the area that he knows of. No redness, swelling, fever, etc. It does not hurt when he presses on it, sits down, or has a bowel movement.

About two days ago, he noticed that for about a half hour after he urinates, he still feels like he has to urinate or that urine is still in his urethra. He hardly ever drinks water, by the way. He has no other urinary symptoms. No blood, pain or difficulty urinating, etc.

My first thought was an enlarged prostate or some other prostate issue. However, he’s 23 with no family history of prostate problems and he really doesn’t have any typical symptoms of this.

Next I thought of a UTI. But that would only explain the urinary symptom. Neither of these explanations address tailbone pain.

These symptoms just don’t seem to go together, and he’s concerned he did something to cause a problem when he penetrated himself. I just don’t know what he could’ve done or how these problems relate. Is it possible that it’s all a coincidence and it’s separate issues altogether?

At what point should he see a doctor? What things come to mind for you upon hearing these concerns?