It is my experience that guys don't really want to know too much about things like this. It makes them uncomfortable. That's not a fault, but it is an indicator to you that sometimes, like now, he probably is feeling it is TMI. It doesn't mean he doesn't care, about you or this, but that he heard enough. He did already weigh in on this and offered that a you might want to talk to your doctor, someone more knowledgeable than he.

He probably wants you to handle it, as it is a (very) personal thing. As you indicated, he's happy to talk to you about anything else, but this. Yes, it is important to you, but he said what he had to say...
BTW, trying to have this sort of 'conversation' via text~at work~ seems inappropriate. This is an 'in person' sort of thing, don't you think?

So, what do you say? Say you are handling it but you are a little scared, you wish he understood your fear & you'll let him know when it's over. I'm sorry for your frustration. Is extracting from him the desired response as good as a spontaneous one?
Just a thought....

Wish you the best in this procedure; I hope this is the right thing for you.